To assess the prevalence of HIV infection and related risk factors among Dutch expatriates returning from assignment in sub-Saharan Africa, Latin America, and South and South-east Asia.From July 1994 to January 1996, a questionnaire on the risks of sexual exposure was completed by 864 respondents, and blood samples were taken.Of the 634 men, 41% reported having sex with casual or steady local partners and 11% with casual or steady expatriate partners, during an average stay of 26 months in the previous 3 years. Of the 230 women, these figures were 31 and 24%, respectively. Of the men with local casual partners (29%), 59% paid for sex at least once. For men as well as women, having sexual contacts abroad was associated with younger age, positive intention prior to departure to have sex abroad, being single at departure, and, only for the men, working for a commercial organization, and feelings of loneliness and boredom. Among men, consistent condom use with casual local partners was 69%, and with casual expatriate partners 63%. Among women, these figures were 64 and 48%, respectively. Consistent condom use with steady local or expatriate partners was much lower. Among men, non-consistent condom use with casual partners was more prevalent if they had been abroad for a longer time, condoms were not taken along from The Netherlands, the country where they were posted was Asian, and the estimated HIV prevalence among the local population was lower. Among the women, non-consistent condom use was more prevalent if condoms were not taken along, and if they did not have the intention before departure to have sex abroad. Of the persons from whom blood could be obtained, one man was HIV-positive. Another man who refused to participate in the study indicated that he was HIV-positive.Although 23% of the expatriates had unprotected sex with partners from endemic areas, very few HIV infections were found. In comparison with a previous study among this population carried out in 1987-1989, which found five out of 1968 expatriates to be HIV-infected, consistent condom use with casual local partners did increase considerably (from 21 to 67%). However, health education is needed to reduce the risk of HIV infection, which should emphasize the sociocultural differences in sexual practices.A survey conducted among 864 Dutch expatriates returning home from assignment in AIDS-endemic areas in sub-Saharan Africa, Latin America, and South and South East Asia revealed a low rate of HIV infection, despite widespread high-risk sexual practices. During an average stay out of the country of 26 months in 1991-96, 41% of the 634 male respondents reported sex with casual or steady local partners and 11% with casual or steady expatriate partners. Among the 230 female expatriates, these rates were 31% and 24%, respectively. 58% of men with casual local partners paid for sex at least once. Among men, consistent condom use was practiced in 69% of encounters with casual local partners and 63% of the time with casual expatriate partners. Among women, these rates were 64% and 48%, respectively. The prevalence of consistent condom use with casual local partners in this study was three times greater than that identified in a study conducted among Dutch expatriates in 1987-89. Condom use with regular local or expatriate partners was substantially lower (16.1-27.8%), however. Inconsistent condom use with casual partners was significantly associated, among men, with being abroad for a longer period of time, failure to bring condoms with them from the Netherlands, posting in an Asian country, and a relatively low estimated HIV prevalence in the local population. Among women, these risk factors were failure to take condoms to their destination and lack of intention at departure to have sex abroad. Only one case of HIV infection was detected in the 847 respondents who underwent serologic testing. Since expatriates function as a bridge between areas with high and low HIV prevalence, educational campaigns that prepare departing workers for differences between the sexual culture at home and abroad and encourage them to take a supply of condoms are recommended.