OBJECTIVE: To describe and analyse the types and circumstances of all natural and non-natural deaths among seamen on board Danish merchant ships. METHODS: Data on 147 cases were obtained from maritime authorities, an insurance company, shipping companies, hospitals, death registers, and death certificates in the period from 1986-93. RESULTS: The 53 natural deaths were dominated by cardiovascular diseases and infectious diseases. Insufficient treatment on board was identified as a contributing factor for death in some cases. Medical advice was not always sought and the advice given was in some cases insufficient. 73 fatal accidents were identified. The incidence of accidents of 5.29/10,000 person-years was 11.5 times higher than the incidence of 0.46/10,000 for the Danish male workforce ashore. 23 accidents (31%) were due to maritime casualties and 26 (36%) were occupational accidents. The remaining 24 (33%) were accidents during off duty hours including six self intoxications. Rough weather, inadequate awareness of safety, lack of use of personal protection devices, and inexperience were associated with many of the fatal injuries directly related to work. Alcohol played a major part in 12 out of 18 fatal injuries occurring during off duty hours. CONCLUSIONS: The maritime workplace was identified as a high risk workplace and in many aspects differs from the conditions ashore. Acute diseases and serious injuries pose special risks to seamen because of a lack of direct access to professional medical care at sea. Primary prevention of certain diseases is needed and possible. Improved training, improved systems of work, improved safety awareness, and greater use of personal protection devices are needed to prevent fatal injuries. Medical training of ships' officers providing medical care on board and specific training of doctors giving medical advise to ships should be improved to meet the needs.