Representing victims of medical malpractice across Ontario
A delayed diagnosis can have devastating consequences. In some cases, a delay in identifying a medical condition allows a disease to progress, reduces treatment options, or leads to permanent injury or death.
In Ontario, a delayed diagnosis may amount to medical malpractice if a physician or hospital failed to meet the accepted standard of care and that failure caused harm.
Not every delay is negligent. This page explains when a delayed diagnosis may support a malpractice claim, what must be proven, and when it makes sense to speak with a medical malpractice lawyer in Ontario.
A delayed diagnosis occurs when a healthcare provider fails to identify a medical condition within a reasonable time, given the patient’s symptoms, history, and available information.
Delays can happen at many stages of care, including:
Failure to recognize concerning symptoms
Failure to order appropriate tests or imaging
Failure to follow up on abnormal results
Failure to refer to a specialist
Failure to act on a diagnosis once it is made
A delay, by itself, is not automatically negligence. Medical malpractice depends on whether the care fell below accepted medical standards and whether the delay caused avoidable harm.
In Ontario, a delayed diagnosis may constitute medical malpractice when a physician or hospital did not act as a reasonable healthcare provider would have acted in similar circumstances.
Examples that may support a claim include:
Repeated patient complaints that were dismissed or not investigated
Failure to order imaging, blood work, or other diagnostic tests despite red flags
Abnormal test results that were not reviewed or followed up
Failure to refer to a specialist when indicated
Misinterpreting or ignoring radiology or pathology reports
Discharging a patient without adequate assessment or safety planning
The focus is not on whether the outcome was bad, but on whether the delay was avoidable and unreasonable based on the information available at the time.
Delayed diagnosis claims most often involve serious conditions where early detection matters. These include:
Cancer (breast, colorectal, lung, gynecologic, prostate)
Sepsis and serious infections
Stroke or transient ischemic attack (TIA)
Heart attack and cardiac conditions
Appendicitis or abdominal emergencies
Internal bleeding or trauma
Pediatric or neonatal conditions
These cases frequently arise from family practice, emergency departments, urgent care settings, and hospital admissions.
Healthcare providers and their insurers commonly defend delayed diagnosis cases by arguing that:
The symptoms were vague or non-specific
The condition was rare or difficult to diagnose
The outcome would have been the same even with earlier diagnosis
The delay was reasonable in the circumstances
Other medical or patient-related factors caused the harm
Because these defences are common, delayed diagnosis cases typically require independent medical experts and careful review of the clinical timeline.
To succeed in a medical malpractice claim based on delayed diagnosis, the plaintiff must prove all of the following:
Standard of Care
What a reasonable physician or healthcare provider should have done in the circumstances.
Breach of the Standard of Care
That the provider failed to act in accordance with accepted medical practice.
Causation
That the delay caused or materially contributed to the injury, progression of disease, or death.
Damages
That the patient suffered compensable harm as a result.
Causation is often the most contested issue. It is not enough to show a delay; it must be shown that earlier diagnosis would likely have changed the outcome.
Medical malpractice claims in Ontario are subject to strict limitation periods.
In most cases, a lawsuit must be started within two years of when the claim was discovered or ought reasonably to have been discovered. Discovery may occur long after the original care, particularly where:
A diagnosis is made years later
The connection between the delay and the harm is not immediately obvious
There are also ultimate limitation periods that can bar claims entirely. Because limitation issues are complex and fact-specific, it is important to seek legal advice as soon as a delayed diagnosis is suspected.
Delayed diagnosis cases are document-heavy. Records that frequently matter include:
Family physician and walk-in clinic notes
Emergency department records
Diagnostic imaging reports
Laboratory results
Consultation and referral letters
Hospital nursing notes
Discharge summaries and follow-up instructions
A detailed timeline built from these records is often essential to evaluating whether negligence occurred.
Depending on the circumstances, compensation in a delayed diagnosis claim may include:
Pain and suffering damages
Income loss and loss of earning capacity
Cost of care and medical expenses
Out-of-pocket expenses
Claims on behalf of family members
Wrongful death damages in fatal cases
Not every case justifies litigation. The seriousness of the harm and the strength of medical evidence are key factors.
Many people assume a delayed diagnosis automatically means malpractice. In reality, many cases are declined because:
The delay did not change the outcome
The standard of care was met despite the delay
The damages are not sufficient to justify the cost of litigation
Expert medical support is unlikely
An honest evaluation at the outset can save families years of unnecessary stress.
Delayed diagnosis cases are among the most complex types of medical malpractice claims. They require careful review of medical records, expert analysis, and an understanding of how Ontario courts assess causation and damages.
If you believe a delayed diagnosis may have caused serious harm or death, a medical malpractice lawyer can assess whether the delay was negligent and whether a legal claim is viable.
Initial case reviews are confidential. Not every case can proceed, but obtaining timely legal advice can help you understand your options and protect your rights.