Causation is the second element a plaintiff must prove in an Ontario medical malpractice claim, after standard of care and before damages. The plaintiff must show that the defendant’s negligence caused the injury, ordinarily by satisfying the “but for” test: but for the negligent act or omission, the injury would not have occurred. The Supreme Court of Canada confirmed this approach in Clements v Clements, 2012 SCC 32, [2012] 2 SCR 181, while recognizing a limited “material contribution to risk” exception in narrow circumstances.
In medical cases, causation is often the most contested element. A plaintiff who proves a clear breach of the standard of care may still lose at trial if expert evidence cannot bridge the gap between the breach and the injury. Lost-chance arguments, delayed-diagnosis fact patterns, and cases involving multiple potential causes raise some of the hardest causation questions in Canadian tort law.
Posts tagged Causation analyze how Ontario courts have approached these issues across obstetrical, oncology, emergency, and surgical fact patterns, including appellate decisions that shape how trial judges instruct themselves on the test.
The Supreme Court of British Columbia dismisses a prophylactic laparoscopic hysterectomy bowel injury claim where the plaintiff led no expert evidence. Informed consent, the modified objective test, and the indispensability of expert evidence.
Dr. Bailey admitted that her management of labour was negligent and that it caused a hypoxic brain injury at birth. The plaintiffs still lost, because they could not prove that the brain injury caused the child’s lasting impairments. JB v Bailey is an Alberta decision, persuasive only in Ontario, but it is a clear reminder that admitted negligence and admitted injury are not the same as proven causation.
Most medical malpractice consultations in Ontario don’t result in lawsuits. An honest look at the four barriers that shape case evaluation in this province.
The Ontario Court of Appeal upheld the trial verdict in Shaw Estate v Handler, affirming the standard of care to recall a patient after critical CT findings.
Ontario midwifery negligence case study: failure to escalate to obstetrical consultation, postpartum hemorrhage, emergency hysterectomy, infertility at 30.
Medical malpractice as an intervening act in MVA cases. A Baines v Abounaja analysis from Paul’s 2025 LSO Motor Vehicle Litigation Summit presentation.
A settlement on behalf of a patient diagnosed with terminal metastatic cancer based on imaging alone, who lived for an extended period under a wrong diagnosis.
Ontario mid-trial ruling adopts but-for phrasing for jury causation questions in delayed diagnosis aneurysm case but declines to require jurors to give reasons.
New Brunswick court holds anesthesiologist negligent in death of 36-year-old patient with severe obesity and sepsis after spinal anesthesia choice and management.
Manitoba Court of Appeal affirms dismissal of delayed colon cancer diagnosis claim. The Benhaim framework on adverse inferences and statistical evidence in causation.
Ontario Superior Court dismisses fatal aortic dissection claim against internist and ED physician. The standards of care for mild aortic dilation and hypertensive chest pain.
Ontario Superior Court finds gynecologic surgeon liable for unrecognized intraoperative bowel injury. The duty to inspect framework in laparoscopic surgery.
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