The purpose of this study was to find out morbidity rate and utilization pattern of medical services of sailors on a voyage. The subjects of this study were 470 sailors who are sailors' trainee and safety-trainee for embarkation in a ship. Data were collected by means of personal survey conducted from September 5 to October 30, 1988. The subjects were sailed 12.6 months on the average. During the voyage, 49.4% of the sailors had sickness more than once, and 24.7%' was unable to work more than a day because of illness. The average monthly morbidity rate was 85.7 per 1,000 and the monthly prevalence rate of disease that was unable to work more than a day was 21.2 per 1,000. The sailors of 40-49 years old had the highest morbidity rate of 103.6 per 1,000/month. The number of days activity restricted due to sickness was 93.4 days per 1,000 persons, and the average duration of illness was 11.2 days per sickness. The proportion of treatment days to sickness days was 48.8%. Considering morbidity unable to work more than a day, the number of those who had traumatic injury were 17.2%, which revealed the highest rate, influenza or cold were 15.5%, and the digestive disease 11.2%. Less than half(42.1%) of patients were treated with medicine kept in the cabin. However, 2.1% was transferred by helicopter and 29L% was treated at hospitals or clinics in nearby port. In the cabin, 67.4% of patients was cured completely.