The social security department of the French national electric and gas company has established a cancer register among a population of about 150,000 active employees based on sick leaves of both short and long duration as well as deaths recorded along with their medical cause. A first study conducted in male workers, aged 20-59, during the 1978-1989 period showed a lower cancer incidence for almost every site of cancer except for leukaemias and others reticuloses tumors of lymphoid and histiocyte tissues, compared with the French general population (SIR = 148 and 218 resp.). Between the 1978-1982 and 1983-1989 periods, a marked decrease (statistically significant) was observed in the incidence of larynx cancer and cancers of all sites usually related with excessive alcohol consumption. During the same period the incidence of pancreatic cancer has almost doubled. Large variations according to socio-economic status were observed for cancers of the lung, the pharynx, the oral cavity and the oesophagus and, also, to a lesser degree, for tumours of the testis and the bladder and leukaemias. The results suggest further studies of occupational factors. Interest and limits of such a compagny register are discussed.