The risk of mortality related to occupation was determined for commercial fishermen in the Canadian Atlantic coast provinces of Nova Scotia, New Brunswick, and Prince Edward Island. The subjects were a cohort of 31,415 fishermen licensed by the Canadian Department of Fisheries during 1975-83. Mortality and cause of death were obtained from the Canada Mortality Data Base and the Marine Casualty Investigation Unit (MCI), and were confirmed by examination of death certificates. Eighty four deaths likely to be related to fishing were recorded over 183,378 person-years of exposure for an annual mortality of 45.8 (95% confidence interval (CI) 36.0-55.6) per 100,000 fishermen. The rate of potential years of life lost up to age 75 was 1583 per 100,000 person-years of exposure. Inclusion of 14 additional deaths, which were possibly related to occupation, would increase these rates further. Bias in this study is likely to underestimate the risks. It is concluded that fishing is one of the most hazardous occupations in terms of mortality related to work.