This study was designed to establish the manner and causes of all fatalities among seafarers who were serving in British merchant shipping between 1 January 1986 and 31 December 1995. Other main aims were to compare mortality rates with workers in other industries and with seafarers in other merchant fleets, and to discuss recommendations for the prevention of occupational mortality. This study was based upon official mortality files with a population of 253 919 seafarer-years at risk. There was a total of 252 fatalities in British merchant shipping during the study period. One hundred and seven of the 252 deaths were due to natural causes, of which 93 (87%) were caused by cardiovascular disease. The relative risk of mortality due to accidents at work (96 fatalities) was 23.9 times higher than for all workers in Great Britain during the same time period (95% confidence interval = 14.0-40.7). The risk of a fatal accident in merchant shipping was also much higher than in other British industrial sectors, such as agriculture, forestry and fishing (relative risk = 4.5), construction (5.5), and manufacturing (22.0). Seafaring was identified as a dangerous occupation compared with shore-based employment. Many of the fatal accidents at work were caused by hazardous working practices and were often preventable, as were the many off-duty accidents and drowning that were caused by seafarers falling into docks when encountering hazardous access to their ships from the shore. Seafarers are also at special risk from acute illnesses since they lack direct access to specialist medical care.