Rule 53.08 of the Rules of Civil Procedure was amended on March 31, 2022 to break a habit. Expert reports were being served late as a matter of course, deadlines were treated as suggestions, pre-trials were wasted, and trials were adjourned. The amendment replaced “leave shall be granted” with “leave may be granted” and added a new precondition: the defaulting party must show a reasonable explanation for the failure.
Four years on, the Divisional Court has told motion judges that the correction can be overdone. In Pelrine v Chung, 2026 ONSC 4362, a panel of Firestone RSJ, Howard RSJ and McKelvey J. allowed a defendant physician’s appeal and granted leave to deliver two late served expert reports that a motion judge had excluded. The holding is short and consequential: the interests of justice run through the whole of rule 53.08, not only its second branch.
The underlying claim
Donna Pelrine developed a rare form of bone cancer in 2015. On the plaintiffs’ allegations, a CT imaging report received in May 2015 recommended radiographic follow-up, and her family physician, Dr. Pin Chung, neither told her about it nor arranged timely follow-up imaging. She was advised of the report in November 2015. Follow-up imaging was performed in December 2015. She then required a hemipelvectomy, which was carried out on April 18, 2016. Further surgeries followed for complications, and Ms. Pelrine died of those complications on May 2, 2016.
None of that has been tried. The action is scheduled to be heard by a jury in September 2026, and the appeal decided nothing about whether Dr. Chung breached the standard of care or caused any loss. What it decided was whether he would be permitted to put expert evidence on causation and damages before that jury.
A chronology that got away from everyone
The claim was issued in April 2018. Discoveries were completed in December 2020. The plaintiffs served a standard of care report in February 2022, a causation report in August 2022 and a damages report in January 2024.
The defence timeline is where the trouble sits. Trial counsel asked the plaintiffs three times, over roughly eighteen months, whether reports would be delivered against the other defendant physicians and whether the action would be pursued against them. He received no answer. The plaintiffs set the action down for trial in December 2023, and neither side complied with rule 53.03(2.2), which requires the parties to agree on a schedule for the exchange of expert reports within 60 days of the action being set down.
Trial counsel then retained a standard of care expert in early 2024, went out of province on a lengthy trial, and fell behind. In September 2024 he learned that the expert had died the previous month without completing a report. A replacement was retained in February 2025. At the June 19, 2025 pre-trial conference, plaintiffs’ counsel confirmed for the first time that the action would be dismissed against every defendant except Dr. Chung. The three responding reports were served on June 24, June 27 and August 19, 2025, all of them more than a year before the scheduled trial date.
What the motion judge decided
The motion judge treated rule 53.08(1) as a strict two-stage conjunctive test. On his reading, a court reaches the prejudice and delay analysis in subrule (1)(b) only if the defaulting party first clears the reasonable explanation hurdle in subrule (1)(a).
He then found the explanation reasonable for the standard of care report, whose delay was partly explained by the expert’s death, but not for the causation and damages reports. Those reports, he found, were not premised on the standard of care opinion, so the death had no domino effect on them. The remaining explanations, principally counsel’s decision to wait until he knew whether the action was proceeding against all the physicians, and his failure to bring in colleagues while he was out of province, were characterized as inattentiveness rather than inadvertence, and inattentiveness was not enough.
Two paragraphs of his reasons became the centre of the appeal. The motion judge acknowledged that his ruling appeared harsh, that all three reports had been served just over a year before trial, and that there was little risk of an adjournment even if all three went in. He said that had he found a reasonable explanation, he would have found the interests of justice favoured admitting the reports. He excluded them anyway because he read the test as conjunctive, and said that if the test had required balancing, his ruling would have been different.
What the Divisional Court held
The Divisional Court allowed the appeal, having already released a June 8, 2026 endorsement to that effect so the September trial date could hold.
The panel accepted that a plain reading of the amended rule is conjunctive and that a reasonable explanation is genuinely required. What it rejected was the sequencing. Rule 1.04, the liberal construction provision, applies throughout the entire rule and not merely to subrule 53.08(1)(b). Prejudice is a separate factor under (1)(b), but the question of prejudice is also inherent in what the interests of justice require, which means it cannot be quarantined from the (1)(a) analysis. An explanation is not to be assessed in a vacuum. It is assessed against the whole of the surrounding circumstances, and, in the court’s formulation, “the rule requires a reasonable explanation, not a perfect explanation.”
The panel was equally direct about the inadvertence and inattentiveness distinction that had done most of the work below. Sorting a lawyer’s default into one category or the other, and making that the determining factor, is too strict, rigid and arbitrary. Mistakes, errors in judgment, and even a deliberate decision to serve a report late that is grounded in a reasonable belief that it was necessary, may all amount to a reasonable explanation, depending on the resulting prejudice, the delay and the rest of the context.
Applied to the facts, that produced a straightforward result. The same explanation had been offered for all three reports and accepted for one. All three were served more than a year before trial, leaving the plaintiffs time to obtain supplementary reports. The trial date was not affected. There was no non-compensable prejudice. The late service was not tactical. Neither side had complied with rule 53.03(2.2), which the court treated as a relevant factor cutting against a purely one-sided allocation of the consequences.
Two authorities did the heavy lifting. Harris v Grand River Hospital, 2026 ONSC 240, 180 O.R. (3d) 273 (Div. Ct.), had already overturned the very reasoning the motion judge relied on, but was released after his decision, so he did not have it. And 1086289 Ontario Inc. (Urban Electrical Contractors) v Welland (City), 2026 ONCA 352, in which a five-judge panel of the Court of Appeal overruled Handley Estate v DTE Industries Limited, 2018 ONCA 324, supplied the broader principle: a rigid rule that mandates an outcome without regard to prejudice or context works against the objective it was built to serve.
The plaintiffs’ argument was not a weak one
It is worth being fair to the respondents, because their position had real force and will be run again.
The 2022 amendment was a deliberate legislative choice to make late service consequential. Its purpose, as the case law after the amendment repeatedly said, was to send a clear message to the bar that reports are to be served on time. On the respondents’ argument, an intentional feature of the new rule is that there will be cases where a client bears the consequences of counsel’s conduct, and reintroducing a general balancing exercise converts the rule back into the escape clause it was designed to eliminate. They also argued that the trier of fact would not be left without causation or damages evidence at all: there is no property in a witness, the plaintiffs’ experts owe a duty of impartiality, and the defence would be free to cross-examine them.
That last point deserves a note. The reasons do not engage with it at length, and it is not obvious that cross-examining an opponent’s expert is a substitute for adducing your own opinion on causation in a case of this complexity. But as an argument about what the amended rule was actually meant to accomplish, it is not frivolous, and counsel opposing a late report should still be making it.
Why the stakes are different in malpractice cases
The panel said expressly that a contextual approach matters most in medical malpractice cases, because either side’s case may turn on whether the expert evidence is admitted. It cited Liu v Wong, 2016 ONCA 366, for the proposition that these cases are complex even where they look simple, and that judges and juries cannot assess standard of care, breach and causation without expert assistance.
That asymmetry is the practical heart of the decision. In most civil actions, excluding a late report is a serious setback. In a malpractice action it is frequently the end of the case, which is why ensuring an expert is permitted to testify at trial is a distinct discipline from finding an expert who will write a helpful report. A framework that produces case-ending consequences for a timing default, in a case where the trial date is not in jeopardy and the opposing party cannot point to prejudice, is disproportionate in a way that the Divisional Court was not prepared to accept.
None of this makes the rule toothless. Reports served late for tactical reasons, or in deliberate disregard of the rule with no justification at all, remain squarely within its reach, and refusing leave in those circumstances remains appropriate. Procedural defaults still end medical malpractice claims outright, as Tookenay v O’Mahony Estate illustrates in a different context. What has changed is that the explanation for the delay can no longer be evaluated in isolation from what excluding the evidence would actually do to the case.
For patients and families
Ms. Pelrine died in May 2016. The claim was issued in 2018 and the trial is set for September 2026. A single interlocutory dispute about the timing of two expert reports consumed a motion, a leave application, an expedited appeal and roughly eighteen months. That is a real feature of this litigation, and anyone considering what a medical malpractice claim in Ontario actually involves should understand that fights of this kind are ordinary rather than exceptional.
The other thing worth taking from the decision is how completely these cases run on expert evidence. It is the reason so many claims are declined at the intake stage, the reason they are expensive, and the reason a scheduling default can matter more than it sounds like it should. The Divisional Court’s instinct here, that a jury deciding whether a delayed cancer diagnosis caused a death should have the relevant expert opinion in front of it, cuts in both directions. It protected a defendant physician in this case. It will protect plaintiffs in the next one.
Donna Pelrine, by her Estate Trustee James Pelrine et al. v Chung et al., 2026 ONSC 4362 (Div. Ct.), released July 30, 2026.
Pelrine v Chung: Late Expert Reports, Rule 53.08, and the Interests of Justice
Rule 53.08 was tightened in 2022 to stop the routine late service of expert reports. In Pelrine v Chung, the Divisional Court held that the correction can be overdone, and that the interests of justice apply throughout the rule rather than only at its second stage. Two excluded defence reports were let in, thirteen months before a jury trial.
Rule 53.08 of the Rules of Civil Procedure was amended on March 31, 2022 to break a habit. Expert reports were being served late as a matter of course, deadlines were treated as suggestions, pre-trials were wasted, and trials were adjourned. The amendment replaced “leave shall be granted” with “leave may be granted” and added a new precondition: the defaulting party must show a reasonable explanation for the failure.
Four years on, the Divisional Court has told motion judges that the correction can be overdone. In Pelrine v Chung, 2026 ONSC 4362, a panel of Firestone RSJ, Howard RSJ and McKelvey J. allowed a defendant physician’s appeal and granted leave to deliver two late served expert reports that a motion judge had excluded. The holding is short and consequential: the interests of justice run through the whole of rule 53.08, not only its second branch.
The underlying claim
Donna Pelrine developed a rare form of bone cancer in 2015. On the plaintiffs’ allegations, a CT imaging report received in May 2015 recommended radiographic follow-up, and her family physician, Dr. Pin Chung, neither told her about it nor arranged timely follow-up imaging. She was advised of the report in November 2015. Follow-up imaging was performed in December 2015. She then required a hemipelvectomy, which was carried out on April 18, 2016. Further surgeries followed for complications, and Ms. Pelrine died of those complications on May 2, 2016.
None of that has been tried. The action is scheduled to be heard by a jury in September 2026, and the appeal decided nothing about whether Dr. Chung breached the standard of care or caused any loss. What it decided was whether he would be permitted to put expert evidence on causation and damages before that jury.
A chronology that got away from everyone
The claim was issued in April 2018. Discoveries were completed in December 2020. The plaintiffs served a standard of care report in February 2022, a causation report in August 2022 and a damages report in January 2024.
The defence timeline is where the trouble sits. Trial counsel asked the plaintiffs three times, over roughly eighteen months, whether reports would be delivered against the other defendant physicians and whether the action would be pursued against them. He received no answer. The plaintiffs set the action down for trial in December 2023, and neither side complied with rule 53.03(2.2), which requires the parties to agree on a schedule for the exchange of expert reports within 60 days of the action being set down.
Trial counsel then retained a standard of care expert in early 2024, went out of province on a lengthy trial, and fell behind. In September 2024 he learned that the expert had died the previous month without completing a report. A replacement was retained in February 2025. At the June 19, 2025 pre-trial conference, plaintiffs’ counsel confirmed for the first time that the action would be dismissed against every defendant except Dr. Chung. The three responding reports were served on June 24, June 27 and August 19, 2025, all of them more than a year before the scheduled trial date.
What the motion judge decided
The motion judge treated rule 53.08(1) as a strict two-stage conjunctive test. On his reading, a court reaches the prejudice and delay analysis in subrule (1)(b) only if the defaulting party first clears the reasonable explanation hurdle in subrule (1)(a).
He then found the explanation reasonable for the standard of care report, whose delay was partly explained by the expert’s death, but not for the causation and damages reports. Those reports, he found, were not premised on the standard of care opinion, so the death had no domino effect on them. The remaining explanations, principally counsel’s decision to wait until he knew whether the action was proceeding against all the physicians, and his failure to bring in colleagues while he was out of province, were characterized as inattentiveness rather than inadvertence, and inattentiveness was not enough.
Two paragraphs of his reasons became the centre of the appeal. The motion judge acknowledged that his ruling appeared harsh, that all three reports had been served just over a year before trial, and that there was little risk of an adjournment even if all three went in. He said that had he found a reasonable explanation, he would have found the interests of justice favoured admitting the reports. He excluded them anyway because he read the test as conjunctive, and said that if the test had required balancing, his ruling would have been different.
What the Divisional Court held
The Divisional Court allowed the appeal, having already released a June 8, 2026 endorsement to that effect so the September trial date could hold.
The panel accepted that a plain reading of the amended rule is conjunctive and that a reasonable explanation is genuinely required. What it rejected was the sequencing. Rule 1.04, the liberal construction provision, applies throughout the entire rule and not merely to subrule 53.08(1)(b). Prejudice is a separate factor under (1)(b), but the question of prejudice is also inherent in what the interests of justice require, which means it cannot be quarantined from the (1)(a) analysis. An explanation is not to be assessed in a vacuum. It is assessed against the whole of the surrounding circumstances, and, in the court’s formulation, “the rule requires a reasonable explanation, not a perfect explanation.”
The panel was equally direct about the inadvertence and inattentiveness distinction that had done most of the work below. Sorting a lawyer’s default into one category or the other, and making that the determining factor, is too strict, rigid and arbitrary. Mistakes, errors in judgment, and even a deliberate decision to serve a report late that is grounded in a reasonable belief that it was necessary, may all amount to a reasonable explanation, depending on the resulting prejudice, the delay and the rest of the context.
Applied to the facts, that produced a straightforward result. The same explanation had been offered for all three reports and accepted for one. All three were served more than a year before trial, leaving the plaintiffs time to obtain supplementary reports. The trial date was not affected. There was no non-compensable prejudice. The late service was not tactical. Neither side had complied with rule 53.03(2.2), which the court treated as a relevant factor cutting against a purely one-sided allocation of the consequences.
Two authorities did the heavy lifting. Harris v Grand River Hospital, 2026 ONSC 240, 180 O.R. (3d) 273 (Div. Ct.), had already overturned the very reasoning the motion judge relied on, but was released after his decision, so he did not have it. And 1086289 Ontario Inc. (Urban Electrical Contractors) v Welland (City), 2026 ONCA 352, in which a five-judge panel of the Court of Appeal overruled Handley Estate v DTE Industries Limited, 2018 ONCA 324, supplied the broader principle: a rigid rule that mandates an outcome without regard to prejudice or context works against the objective it was built to serve.
The plaintiffs’ argument was not a weak one
It is worth being fair to the respondents, because their position had real force and will be run again.
The 2022 amendment was a deliberate legislative choice to make late service consequential. Its purpose, as the case law after the amendment repeatedly said, was to send a clear message to the bar that reports are to be served on time. On the respondents’ argument, an intentional feature of the new rule is that there will be cases where a client bears the consequences of counsel’s conduct, and reintroducing a general balancing exercise converts the rule back into the escape clause it was designed to eliminate. They also argued that the trier of fact would not be left without causation or damages evidence at all: there is no property in a witness, the plaintiffs’ experts owe a duty of impartiality, and the defence would be free to cross-examine them.
That last point deserves a note. The reasons do not engage with it at length, and it is not obvious that cross-examining an opponent’s expert is a substitute for adducing your own opinion on causation in a case of this complexity. But as an argument about what the amended rule was actually meant to accomplish, it is not frivolous, and counsel opposing a late report should still be making it.
Why the stakes are different in malpractice cases
The panel said expressly that a contextual approach matters most in medical malpractice cases, because either side’s case may turn on whether the expert evidence is admitted. It cited Liu v Wong, 2016 ONCA 366, for the proposition that these cases are complex even where they look simple, and that judges and juries cannot assess standard of care, breach and causation without expert assistance.
That asymmetry is the practical heart of the decision. In most civil actions, excluding a late report is a serious setback. In a malpractice action it is frequently the end of the case, which is why ensuring an expert is permitted to testify at trial is a distinct discipline from finding an expert who will write a helpful report. A framework that produces case-ending consequences for a timing default, in a case where the trial date is not in jeopardy and the opposing party cannot point to prejudice, is disproportionate in a way that the Divisional Court was not prepared to accept.
None of this makes the rule toothless. Reports served late for tactical reasons, or in deliberate disregard of the rule with no justification at all, remain squarely within its reach, and refusing leave in those circumstances remains appropriate. Procedural defaults still end medical malpractice claims outright, as Tookenay v O’Mahony Estate illustrates in a different context. What has changed is that the explanation for the delay can no longer be evaluated in isolation from what excluding the evidence would actually do to the case.
For patients and families
Ms. Pelrine died in May 2016. The claim was issued in 2018 and the trial is set for September 2026. A single interlocutory dispute about the timing of two expert reports consumed a motion, a leave application, an expedited appeal and roughly eighteen months. That is a real feature of this litigation, and anyone considering what a medical malpractice claim in Ontario actually involves should understand that fights of this kind are ordinary rather than exceptional.
The other thing worth taking from the decision is how completely these cases run on expert evidence. It is the reason so many claims are declined at the intake stage, the reason they are expensive, and the reason a scheduling default can matter more than it sounds like it should. The Divisional Court’s instinct here, that a jury deciding whether a delayed cancer diagnosis caused a death should have the relevant expert opinion in front of it, cuts in both directions. It protected a defendant physician in this case. It will protect plaintiffs in the next one.
Donna Pelrine, by her Estate Trustee James Pelrine et al. v Chung et al., 2026 ONSC 4362 (Div. Ct.), released July 30, 2026.
Paul Cahill
Partner, Davidson Cahill Morrison LLP | LSO Certified Specialist in Civil Litigation
Paul represents victims of medical malpractice across Ontario, with trial experience including a $11.5M jury verdict in a birth injury case. He is recognized in Best Lawyers in Canada and serves as trial counsel to other lawyers on complex medical negligence matters.
About PaulMore on medical malpractice in Ontario.
Other articles by Paul exploring the conditions, decisions, and systems behind preventable medical harm.
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