Abstract A recent portrait of occupational exposure in Québec to 38 known or probable carcinogens proved of great interest to occupational health and safety (OHS) stakeholder, who expressed a need for more in-depth analysis of the situation in Québec. This report aims to meet that need, providing an analysis by industries and subsectors and identifying occupational groups of particular concern in the case of 41 substances classified as carcinogenic. Studied were substances classified as having a “known” or “suspected” carcinogenic effect in humans (C1 and C2 respectively) or a “known” carcinogenic effect in animals (C3) according to Schedule 1 of the Regulation respecting occupational health and safety, or as “carcinogenic to humans” or “probably carcinogenic to humans” (groups 1 and 2a, respectively) according to the International Agency for Research on Cancer. The number of workers potentially exposed to each carcinogen was obtained by applying the percentage of exposed workers in a given industry, calculated from various data sources, to the number of people working in that industry in Québec according to the 2011 National Household Survey conducted by Statistics Canada. The information on exposure was largely extracted from data compiled as a part of the CARcinogen EXposure Canada (CAREX Canada) project, which takes occupation and industry into account. Data from the 2008 Enquête québécoise sur la santé de la population (Québec population health survey) and the Enquête québécoise sur des conditions de travail, d’emploi et de santé et de sécurité du travail (Québec survey on working, employment and OHS conditions) were used to check some of the results obtained with the CAREX Canada data. For some carcinogens, the exposure data came from two French sources: SUMER 2010, a voluntary survey of occupational health physicians concerning medical surveillance of occupational risk exposure, conducted by the labour branch and statistics service of France’s ministry of labour, employment, occupational training and social dialogue; and the job-exposure matrices developed through MATGÉNÉ, a program to develop job-exposure matrices in the general population implemented by France’s institute for public health surveillance (InVS). Exposure percentages were estimated independently of exposure levels. Based on this approach, the 10 carcinogenic substances or conditions to which the greatest proportion of Québec workers are exposed are night work, including occasional night work (14.2%), sunlight (6.6%), diesel exhaust (4.9%), mineral oils (2.4%), benzene (2.1%), polycyclic aromatic hydrocarbons (HAPs) (2.0%), silica (2.0%), wood dust (1.9%), lead or its organic compounds (1.6%) and ionizing radiation (1.2%). Note that the percentage of workers exposed to night work reported here is much more realistic than that reported in our earlier report (6.6%), obtained from another data source. Based on these percentages, it is estimated that at least 242,300 Québec workers are exposed to solar radiation and close to 180,000 to diesel exhaust on the job. In addition, over 50,000 are exposed to carcinogens in each of the following sectors: manufacturing, transportation and warehousing, and health care and social assistance. Though multiple exposures occur in many subsectors, those where more than 20 different carcinogens are found are concentrated in four particular industries: manufacturing, construction, other services (repair and maintenance; personal and laundry services; etc.) and healthcare and social assistance. These data do not indicate the number of different carcinogens to which any given worker is exposed in these industries and subsectors, but they do show that the potential for multiple exposure is very real. Multiple exposure is a particular concern for skilled trades (machine operators, welders, welding and brazing machine operators) in chemical, plastics and metal manufacturing, and professional, scientific and technical services, and well as for general labourers in a number of subsectors. A breakdown of the data by sex shows that more women are exposed to carcinogens in healthcare and social assistance (night work; ionizing radiation; cytostatic drugs, that is, medicine toxic to cells; and solar radiation). A higher proportion of men are exposed in agriculture, forestry, hunting and fishing, mining, oil and gas extraction, construction, utilities, manufacturing and transportation and warehousing. These industries are characterized in particular by exposure to night work, solar radiation and diesel exhaust. Exposure to PAHs, diesel exhaust, benzene and solar radiation occurs in most industries where young workers constitute a considerable portion of the labour force, including retail trade, arts, entertainment and recreation and accommodation and food service. Exposure to diesel exhaust and solar radiation occurs in most subsectors where older workers are employed (³ 55 years of age), particularly in school and employee bus transportation. In five major sectors, more than 90% of the enterprises are small businesses (less than 20 employees): agriculture, forestry, hunting and fishing; construction; real estate and rental and leasing; professional, scientific and technical services; and other services (except public administration). The carcinogens in these sectors include solar radiation, night work (including occasional), diesel exhaust, wood dust and ionizing radiation. Despite their limitations, the estimates obtained are useful indicators of the extent of Québec workers’ potential exposure to carcinogens depending on industry and occupational group and can provide guidance on preventive measure for OHS professionals and decision-makers. Cancers take years to develop, and it can be difficult to establish a link between a cancer and a given occupational exposure. The best preventive strategy is thus to determine where carcinogens are found in the workplace and then use the same approach as for any occupational hazard, that is, application of the ALARA (as low as reasonably achievable) principle, also called the ALARP (as low as reasonably practicable) principle.