Surveillance for acquired immunodeficiency syndrome (AIDS) in Kinshasa, Zaire, was initiated in July 1984, using a modified version of the case definition developed by the Centers for Disease Control. During the first eight months, 332 patients met all clinical and laboratory criteria; surveillance information was available for 295 (89%) of these patients. Of the sera tested from these patients, 99% had antibodies to human T-cell lymphotropic virus type III/lymphadenopathy-associated virus by both enzyme-linked immunosorbent assay and Western blot procedures. The male-female case ratio was 1:1.1; the mean age of patients was 33.6 years (median, 32 years; range, 1.5 to 64 years); and men were significantly older than women (mean, 37.4 vs 30.0 years). The estimated incidence rate for adults in Kinshasa is 380 cases per 1 million people per year. Peak age-specific incidence rates for men and women occurred among the 30- to 39-year age group, although the rate for men in this age group was 24% higher than the rate for women (786 vs 601 per 1 million). A reasonable estimate of the current annual incidence of AIDS is 550 to 1,000 cases per 1 million people. Surveillance of AIDS in Zaire provides important information on transmission patterns and rates in Africa.