Representing victims of medical malpractice across Ontario
Medical malpractice claims in Ontario are subject to strict limitation periods. If a claim is not started in time, the court may refuse to hear it—regardless of how serious the negligence or harm may be.
This page explains how limitation periods work in Ontario medical malpractice cases, when the clock starts running, and why seeking legal advice early is so important.
A limitation period is a legal deadline for starting a lawsuit. Once the limitation period expires, a claim is usually barred permanently.
In medical malpractice cases, limitation periods are often one of the most important—and most misunderstood—issues.
In most Ontario medical malpractice cases, a lawsuit must be started within two years of when the claim was discovered or ought reasonably to have been discovered.
This does not always mean two years from the date of treatment.
Instead, the clock usually starts when a person knew—or reasonably should have known—that:
An injury occurred
The injury was caused by medical care or a failure to provide care
A legal proceeding would be an appropriate way to seek a remedy
This is often referred to as the “discovery rule.”
In medical malpractice cases, discovery can occur at different times depending on the facts.
Discovery may occur when:
A serious complication develops unexpectedly
A diagnosis is finally made after a delay
A patient learns that test results were missed or not followed up
Medical records reveal earlier warning signs
An expert advises that care may have been negligent
Because discovery is fact-specific, determining the correct limitation date can be complex.
Delayed diagnosis cases often raise difficult limitation issues.
In these cases, discovery may occur:
When the correct diagnosis is finally made
When the patient learns the condition was present earlier
When it becomes apparent that earlier diagnosis may have changed the outcome
The limitation period does not necessarily start at the first medical visit. It often starts much later, once the connection between the delay and the harm becomes reasonably apparent.
In addition to the two-year discovery-based limitation period, Ontario law also imposes ultimate limitation periods.
In many cases, a claim may be barred if it is not started within a fixed number of years from the act or omission itself—even if the injury was not discovered until later.
Ultimate limitation periods can be complicated and may depend on:
the nature of the claim,
the age of the patient,
whether the claim involves a minor or incapable person,
and transitional rules.
These rules can permanently bar claims, which is why delay can be dangerous even when discovery is unclear.
Special rules apply to minors.
In some circumstances:
limitation periods may be suspended while a person is under 18,
but this is not automatic in every case,
and there may still be deadlines related to litigation guardians or court appointments.
Because these rules are technical, legal advice is essential where a child may have been injured.
If a person is mentally incapable of starting a lawsuit, limitation periods may be suspended until:
capacity is regained, or
a litigation guardian is appointed.
However, proving incapacity and triggering suspension is not always straightforward. These issues often become contested.
In medical malpractice cases, defendants often argue that:
the claim was discovered earlier than alleged,
the patient should reasonably have known sooner,
sufficient information existed to start a claim earlier.
Because limitation issues can decide a case before the merits are ever heard, they are frequently litigated.
Patients and families often delay speaking to a lawyer because they are:
waiting for explanations from doctors or hospitals,
pursuing complaints or investigations,
focused on treatment or recovery,
unsure whether negligence occurred.
Unfortunately, waiting for clarity can allow limitation periods to expire.
Internal hospital reviews, complaints, and investigations do not stop the limitation clock.
Medical records often play a central role in determining:
when a claim was discovered,
what information was available at different times,
whether earlier discovery should reasonably have occurred.
Delays in obtaining or reviewing records can complicate limitation analysis.
Speaking with a medical malpractice lawyer early can help:
identify potential limitation issues,
preserve claims before deadlines expire,
determine whether immediate steps are required,
avoid irreversible loss of legal rights.
Seeking advice does not mean a lawsuit must be started immediately—but it helps ensure that options remain available.
If you are unsure whether a limitation period may apply:
do not assume you have time,
do not rely on informal assurances,
seek legal advice as soon as possible.
Even experienced lawyers often treat limitation periods cautiously, because missing a deadline can end a claim entirely.
Limitation periods in Ontario medical malpractice cases are strict and unforgiving. They are often decisive, and they do not pause simply because answers are slow to emerge.
Understanding and addressing limitation periods early is essential to protecting legal rights.
If you have concerns about negligent medical care, a medical malpractice lawyer can assess potential limitation issues and advise on next steps before it is too late.