To evaluate acquired immunodeficiency syndrome (AIDS) in central Africa a prospective study was done in Kigali, Rwanda, where Kaposi's sarcoma (KS) is endemic. During a 4 week period, 26 patients (17 males and 9 females) were diagnosed. 16 patients had opportunistic infections, associated with KS in only 2; 1 had multifocal KS alone; and 9 had clinical conditions consistent with prodromes of AIDS. All patients had severe T-cell defects characterised by cutaneous anergy, a striking decrease in the number of helper T cells, and a decreased OKT4:OKT8 ratio (mean 0.27). 21 of the 22 adult patients were living in urban centres and many of them were in the middle to upper income bracket. Most of the men were promiscuous heterosexuals and 43% of the females were prostitutes. No patient had a history of homosexuality, intravenous drug abuse, or transfusion in the previous 5 years. This study suggests that AIDS is present in central Africa as an entity probably unrelated to the well-known endemic African KS. An association of an urban environment, a relatively high income, and heterosexual promiscuity could be a risk factor for AIDS in Africa.