In an area endemic for visceral leishmaniasis, 16 patients with human immunodeficiency virus (HIV) infection developed the disease. All belonged to populations at risk for AIDS (15 were intravenous drug abusers). Five patients fulfilled the criteria for full-blown AIDS, and two more fulfilled them after diagnosis of leishmaniasis. All presented with the classic manifestations of visceral leishmaniasis, but leishmania serology was negative in 15 patients (93%). Leishmania donovani amastigotes were identified in the bone marrow in all cases. Most patients responded initially to treatment with pentavalent antimonial drugs, but seven (43%) followed a chronic course, with multiple relapses in five, despite alternative treatments. Visceral leishmaniasis occurred in patients with different levels of depression of the CD4 to CD8 lymphocyte ratio. Mortality was 37% (six patients) and was independent of the chronic-relapsing course of the disease. In no case was leishmaniasis the primary cause of death. Our data establish that visceral leishmaniasis is an opportunistic infection in HIV-infected patients, and we suggest that in endemic areas it should be considered an indicator disease for the diagnosis of AIDS.