An occupational disease is any chronic ailment that occurs as a result of work or occupational activity. An occupational disease is typically identified when it is shown that it is more prevalent in a given body of workers than in the general population, or in other worker populations. Occupational hazards that are of a traumatic nature (such as falls by roofers) are not considered to be occupational diseases. Under the law of workers' compensation in many jurisdictions, there is a presumption that specific disease are caused by the worker being in the work environment and the burden is on the employer or insurer to show that the disease came about from another cause.

Some well known occupational diseases include:

• Asbestosis among asbestos miners and those who work with friable asbestos insulation.
• Black Lung Disease among coal miners
• Carpal Tunnel Syndrome among persons who work in the poultry industry and who do data entry.
• Radiation sickness among persons who work in the nuclear industry.
• Phossy jaw and Radium jaw among Matchgirls and Radium dial painters, respectively.
• Byssinosis among workers in parts of the cotton textile industry