Most chemical carcinogenic agents are industrial. About 4% of all cancers have an occupational origin, but the percentage is higher in exposed populations. Evidence of carcinogenicity is provided by epidemiological studies, animal experiments and other biological sources like experimental mutagenesis. The IARC (International Agency for Research on Cancer) classification and the European Union classification of carcinogenic agents for humans are useful for prevention and regulation. Some cancers are classified as occupational diseases but only a few persons receive compensation given the difficulties of aetiologic diagnosis and the frequent absence of declaration.