The infrequent occurrence of perinatal transmission and horizontal transmission of HBV during early infancy causes a high degree of susceptibility among Dutch young adults. To these young adults a stay in an area where HBV is hyperendemic could mean a risk of hepatitis B infection. In order to determine the incidence of HBV infection among Dutch expatriates posted in a hyperendemic area, a study has been carried out between September 1987 and December 1991. In a group of 555 Dutch expatriates, with a mean age of 33,5 and a mean stay in sub-Saharan Africa of two years, 19 new infections (3.4%) were found. The incidence rate was 1,8 HBV infections per 100 person-years. The incidence was independent of age. Although the incidence rate was higer for women (2.6 HBV infections per 100 person-years) than for men (1.2 HBV infections per 100 person-years) the difference did not reach statistical significance (incidence rate ratio 2.2 90%CL 0.7-7.4). The area of residence proved to effect the incidence. Respondents posted in the northern part of sub-Saharan Africa, had a higher risk of becoming infected, compared to the other parts of sub-Saharan Africa (incidence rate ratio 2.7 90%CL 1.0-7.3, with the central/eastern part as reference). In the study population heterosexual contacts with African partners during the stay in Africa were reported frequently (27%). About 11% of all respondents had a (para)medical profession, of whom 31% reported blood contact in Africa. Other risk factors such as homosexual contact, blood transfusion in Europa or Africa and intravenous drug use were reported infrequently. Without corrections for influence of other risk factors and potential confounders, statistic significant associations with the HBV incidence were found for blood contact during work (incidence rate ratio=5.2 90%CL 2,0-13,4), a (para)medical profession (ratio=2,9 90%CL 1,2-6,8) and, only for female respondents, living with an African life partner (ratio=4,5 90%CL 1,4-15,0). Also, there was an indication of an increased risk for respondents who were injected in Africa by unqualified persons. Among these Dutch expatriates, sexual and occupational risk factors were common. The risk of HBV infection among the Dutch expatriates proved to be increased during the stay in sub-Saharan Africa. The availability of an effective HB-vaccine offers an opportunity for prevention of HBV infections among Dutch expatriates abroad. The results of this study justify the widening of the indications for vaccination against HBV, in 1991 by the Department of the Chief Medical Officer (GHI).