Visceral leishmaniasis (kala-azar) is a worldwide disseminated protozoal infection primarily transmitted by sand flies. Because host defense against this intracellular infection is T-cell-dependent, kala-azar has predictably joined the list of AIDS-related opportunistic infections in endemic areas. The vast majority of patients with AIDS-associated kala-azar are currently found in southern Europe (the Mediterranean basin, especially Spain in injection drug users); future cases will inevitably arise in other endemic regions including India, East Africa and Sudan, and Brazil. In CD4 cell-deficient HIV-infected individuals, kala-azar likely represents recrudescence of previously controlled asymptomatic infection; in drug users, newly acquired infection may result from transmission via shared needles. Coinfected patients are frequently parasitemic and may show atypical clinical presentations, unusual multi-organ involvement, and absent antileishmanial antibodies. Diagnosis is made by microscopic examination or culture of aspirate or biopsy of any involved tissue (primarily bone marrow) or by blood smear or culture. Conventional treatment (pentavalent antimonials) induces initial remission in about 50% of patients; amphotericin B and its new lipid formulations appear more active. If suppressive maintenance therapy is not used, relapse within 1 year is typical. In AIDS patients with a first episode of visceral kala-azar, up to 25% die within 1 month if treatment is stopped. Optimal primary and secondary prophylaxis for AIDS-related kala-azar remain to be determined; life-long maintenance therapy is becoming an accepted approach.