A cohort of 431 male cryolite workers employed for at least six months between 1924 and 1961 was identified from personnel records at the Copenhagen cryolite factory. During this period, heavy fluoride exposure resulted in at least 74 cases of skeletal fluorosis. All workmen in the cohort were followed up in Denmark until July 1, 1981. During 1941-1981, 206 men died, while only 149.3 deaths were expected from national mortality statistics. Significant excesses were seen in the following causes of death: violent death and all cancers, in particular cancer of the respiratory system. When compared with specific mortality rates for the Copenhagen area, violent death (and suicide taken alone) remained in significant excess among employees hired before 1940. Cancer morbidity data for the 35-year period 1943-1977 showed 78 cases of malignant neoplasms in the cryolite workers against 53.2 expected for Denmark as a whole and 67.9 for Copenhagen. The excess was almost entirely due to an excess number of respiratory cancers. Cancer morbidity showed no apparent correlation with length of employment or time from first exposure. Because detailed information on predictors for respiratory cancer was unavailable, a possible residual effect of fluoride cannot be excluded. However, any major carcinogenic effect of heavy fluoride exposure would be very unlikely.