Working conditions are a major determinant of public health. They are also one of the most difficult health determinants to change. In the department of Seine-Saint-Denis, which is characterized by high excess mortality among manual laborers, Inserm and the departmental council have been conducting action research on occupational cancers for the past eight years. Based on a detailed survey of more than 900 cancer patients, the study reveals high exposure of workers to carcinogens at certain sites and a major lack of information and training, as highlighted by Michèle Vincenti-Delmas and Annie Thébaud-Mony. This action research has also helped improve the reporting and recognition of occupational cancers.