The prevalence of antibodies to human immunodeficiency virus (HIV) was determined in the relatives, friends, and sex partners of AIDS patients in Haiti and in other unrelated Haitian population groups. Among contacts of AIDS patients, HIV seroprevalence was highest among sex partners of the opposite sex (55%) and lowest among female relatives and friends (9%) of female AIDS patients. Male relatives and friends of male AIDS patients had a seroprevalence rate of 19% and also had a history of multiple heterosexual partners and frequent contact with prostitutes. The HIV seroprevalence rate among unrelated groups of Haitian adults ranged from 2% in rural healthy adults to 22% among tuberculosis patients to a high of 49% among Haitian prostitutes. This seroprevalence pattern suggests that HIV infection is widespread in Haiti and that heterosexual activity plays a major role in transmission.