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.
How to choose, vet and instruct experts in an Ontario medical malpractice case. From Paul’s October 2026 presentation at Osgoode Professional Development’s Anatomy of a Medical Malpractice Case.
The Supreme Court of British Columbia dismisses a maxillomandibular advancement claim brought by a self-represented plaintiff. An American expert who could not identify the Royal College of Dentists of Canada, a seven-hour video log that contradicted the plaintiff’s trial evidence, and an adverse inference the court declined to draw.
The Court of Appeal for Ontario dismisses Dr. Wang’s appeal in Bradley v Wang, upholding findings that a tetanus vaccine was injected in the wrong part of the arm, that the misplacement caused an adhesive capsulitis, and that no mitigation defence was made out. The decision confirms that counterfactual proof can be assembled from evidence excluding the competing explanation, and that a defendant who cannot show suitable alternative work was available loses the mitigation argument regardless of the plaintiff’s own efforts.
The Court of Appeal for Ontario dismisses Dr. Cavanagh’s causation appeal in Ibrahimova v Cavanagh, upholding findings about what would have happened at a tertiary hospital the patient never reached on the relevant day. The decision confirms that a plaintiff can prove a counterfactual treatment path through a specialist from the receiving discipline, without institutional witnesses, and that a defendant who calls no expert in that specialty is unlikely to recast the resulting findings as speculation.
Some of the most common beliefs about medical malpractice in Ontario are simply wrong, and they cut both ways: pushing some people toward hopeless claims and others away from good ones. Here are the misunderstandings I see most often, set against how the law actually works, from what counts as negligence to limitation periods, College complaints, causation, and the cap on damages.
Norman Clarey nearly died after a bowel resection led to a failed anastomosis and a permanent stoma. A Prince Edward Island court nonetheless dismissed his negligence, breach of contract, and informed consent claims, finding Dr. Gillis met the standard of care throughout and that causation was not proven. As an out-of-province decision it is persuasive but not binding in Ontario, though it applies largely Ontario and Supreme Court of Canada authority.
A new report finds one in 10 admitted patients now spend more than 48 hours waiting in the emergency department, and roughly 16,000 died while waiting for care last year. But a broken system is not the same as a winnable malpractice claim. Here is where an ER delay can cross into negligence in Ontario, and where it cannot.
The Court of Appeal dismisses the appeal in Brown v Meaney, upholding findings that two pediatric neurologists breached the standard of care and the duty to obtain informed consent when they abandoned a pyridoxine trial in an infant with a rare epilepsy. The decision affirms that a defensible first impression does not excuse the failure to revisit it, and that causation need not be proven with scientific precision.
An Alberta court found that an urgent C-section taking 101 minutes fell below the standard of care, that two physicians’ combined 50 minutes of unnecessary delay was not a defensible judgment call, and that the delay caused a child’s cerebral palsy. A look at the timeliness standard, the causation reasoning, and why this Alberta decision is persuasive, not binding, in Ontario.
How surgical negligence claims succeed or fail. A 2026 OTLA Spring Conference paper on never events and recognized complication cases.
Yes, you can sue for medical malpractice in Ontario. The harder question is whether you should. After two decades of these cases, the candid advice for many prospective clients is to think very carefully before going forward, and in some cases, not to go forward at all.
In Forget v Gibb, 2026 ONSC 626, the Ontario court dismissed a surgical negligence claim and delivered a sharp critique of the plaintiff’s expert.
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