Occupational factors that may increase the risk of cancer are often studied in isolation from one another, even though multiple exposure to carcinogens is a reality. Multiple exposure to carcinogens among the French workforce was estimated as part of the Multi-expo project by Santé publique France using data from the 2009–2010 Sumer survey (Medical Surveillance of Occupational Risk Exposures) conducted among 48,000 employees. This survey by the Ministry of Labor provides a description of a wide range of occupational exposures to hazards or work conditions that may be harmful to workers’ health. Three types of carcinogenic hazards were selected: carcinogenic chemical agents (classified as known or probable carcinogens and the most commonly used, totaling 24), ionizing radiation, and night work among women (at least 45 nights per year). The exposure considered is that reported by the occupational physician during an interview with the employee in the course of the last week worked and refers to the presence of a hazard at the workplace. The proportion of employees exposed to a set of carcinogenic hazards is obtained by summing the binary exposure indicators defined for each carcinogen (present/absent) and quantified across the detailed economic sectors and occupational groups. In France, in 2009–2010, 12.0% of employees (~2.6 million, 2 million men and 600,000 women) were exposed to at least one carcinogen (chemical or non-chemical), and approximately 757,000 employees were exposed to at least two carcinogens (i.e., 30% of those exposed). The risks of overestimating and underestimating these numbers are discussed. The sectors and occupational groups most affected are highly specific, with significant differences by gender. They are primarily men (78%), particularly workers in construction and public works, maintenance, metalworking, transportation, and auto repair. In these occupational activities, the four most common carcinogens are: diesel engine emissions, crude mineral oils, wood dust, and crystalline silica. Women of childbearing age (