CAREX is an international information system on occupational exposure to known or suspected carcinogens, built within the framework of the Europe Against Cancer Programme of the European Union. It provides estimates of the number of exposed workers by country, industry, and agent, including data about 139 agents evaluated by the International Agency for Research on Cancer (group 1 and 2A agents, plus selected group 2B ones), across 55 industries classified according to UN-ISIC revision 2. The 1990-3 occupational exposures to these agents were estimated for the fifteen countries of the European Union in two steps. At first, estimates were generated on the basis of the national workforce data, and of the exposure prevalence estimates from two reference countries: Finland and the USA. These estimates are adjusted by economic structure, but they do not take into account country specific patterns of exposure to carcinogens. For selected countries, among which Italy, it was possible to correct these estimates by national experts, who were invited to allow for the exposure patterns that they considered specific to their countries. According to the estimates for Italy, there were about 4.2 million workers, i.e. 24% of the work force, exposed to the agents included in CAREX, with some 5.5 million exposures. The most common exposures were: environmental tobacco smoke (770,000 exposed workers), solar radiation (550,000), diesel engine exhaust (550,000), asbestos (350,000), wood dust (300,000), crystalline silica (260,000), lead and inorganic lead compounds (220,000), benzene (180,000), hexavalent chromium and compounds (130,000) and PAHs (130,000).