Background: The risk of acquiring HIV-1 and HIV-2 infections among expatriates in, and travelers to, West Africa is not known. The objective of the study was to examine the risk of human immunodeficiency virus type 1 and type 2 (HIV-1 and HIV-2) infections among Peace Corps volunteers in West Africa. Methods: A cross-sectional serosurvey was carried out in 18 West African countries. Subjects were 2491 returning Peace Corps volunteers. The main outcome measure was seropositivity for HIV-1 and HIV-2 antibodies. Results: From March 1988 through February 1993, of 2491 study participants, no HIV-2 infections were detected, but three HIV-1 infections were. All three HIV-1-infected persons reported having had unprotected sex with host-country national partners. Conclusions: Results suggest that although persons having unprotected sex with partners from countries with a high prevalence of HIV-1 are at risk for acquiring the infection, casual transmission of HIV-1 or HIV-2 is extremely unlikely.