Given the frequency of cancers, prevention is based on knowledge of the causes. Experts estimate the proportion of cancers attributable to work at around 5 %. If it is shown that exposure at work is involved, the patient can claim compensation for an occupational disease. In order for the occupational origin to be identified, it is important to know which jobs/sectors of activity are possibly at risk. The aim of this article is to present the six main cancer sites for which a link with occupational exposure has been documented, to specify the causes of the under-reporting of occupational cancers, the role of the treating physician working in a multidisciplinary network, and the tools and practical advice for optimizing the support to patients/their relatives.