A cohort of 30,940 male and 11,529 female seafarers registered in the files of Seafarers' Pension Fund in Finland was followed up through the Finnish Cancer Registry for cancer in 1967-92. Among male seafarers, there were 1,199 cases of cancer, which corresponds to the average cancer incidence in Finnish men. There was a statistically significant excess of non-melanoma skin cancer (standardized incidence ratio [SIR] = 1.8, 95 percent confidence interval [CI] = 1.2-2.5) and mesothelioma (SIR = 2.9, CI = 1.2-5.6) in the follow-up category of 20 or more years since the first employment. Alcohol-related cancers were increased among seafarers (SIR for cancer of the mouth and pharynx = 1.5; esophagus = 1.4; and liver = 1.5; combined CI = 1.1-1.9). Deck crews had a significantly high risk of cancer of the pancreas (SIR = 2.0) and also prostate after 10 years since first employment (SIR = 1.6). Occupational asbestos exposure among seafarers is likely strong enough to cause excess cases of mesothelioma but not of lung cancer. Occupational exposures also may be associated with increased risk of cancers of the kidney, pancreas, prostate and old-age brain cancer in some of the main occupational categories. Cumulative ultraviolet radiation likely doubles the risk of non-melanoma skin cancer among older men and repeated sunburns that of skin melanoma in ages below 30 (SIR among deck and engine crew = 4.6, CI = 3.1-6.5). Female ship personnel had a significantly elevated total cancer risk (observed number of cases = 732) which increased over follow-up time (SIR in the category > or = 20 years since the first employment was 1.3, CI = 1.1-1.5). This excess was attributable primarily to lung cancer (SIR = 2.6, CI = 2.0-3.3). Also cancers of the cervix uteri, vulva, and vagina showed significant excess after 10 to 20 years since first employment aboard.