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Occupational disease

What is an occupational disease? It is a disease caused by work, either by the work environment or the tasks related to it.


An occupational disease must be specific to a type of work or directly related to the risks associated with that work. For example, a lung disease such as asbestos is characteristic of work where workers are exposed to asbestos.

Criteria for an occupational disease

As in the case of a work accident, an occupational disease can be contracted out of or in the course of work. It is the CNESST that determines, based on various criteria, whether or not it is an occupational disease.

Disease contracted out of work

When contracted out of work, the disease developed while the worker was performing the tasks for which they are employed (for example, a factory worker who becomes deaf after working in a noisy factory environment for many years).

Disease contracted in the course of work

The occupational disease developed when the worker was performing tasks other than those they normally do. These tasks may be directly or indirectly related to their work.


If a worker believes that their disease is related to their work, they must inform their treating healthcare professional, who will provide them with a medical certificate to attach to the Worker’s claim form.

The worker’s disease will be recognized as an employment injury if, as the case may be:

  • it is listed in the Regulation respecting occupational diseases and the worker meets the specific conditions related to the disease
  • the worker shows that their disease is characteristic of the work they are doing or have done in the past, or that it is directly related to the specific risks associated with the work

Making a claim in the event of an occupational disease

In the case of an occupational disease, the worker may be entitled to indemnities, healthcare services and rehabilitation if their claim is accepted. They must fill out the Worker’s claim form and the appendix corresponding to their medical situation as determined with their treating healthcare professional. The CNESST will then analyze the admissibility of the claim.

The worker must fill out and submit the Worker’s claim form and the corresponding appendix within 6 months following, as the case may be:

  • the diagnosis of the occupational disease confirmed by their treating healthcare professional
  • the moment when they became aware of the probable relationship between their disease and their work

In the case of a non-work-related illness, if the worker has to take time off work, their employment relationship is protected.

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