Despite being a well-known pathogen for immunocompromised patients, Legionella pneumophila has infrequently been described in persons with infection due to human immunodeficiency virus (HIV). Since 1986, we have identified eight cases of legionella pneumonia among seven HIV-infected persons enrolled in the HIV Natural History Study of the U.S. Air Force. The median CD4+ T cell count for these patients was 83/mm3; 50% of the cases occurred in persons for whom AIDS was previously diagnosed, and five of the cases were nosocomial. Six of the patients had coexistent pulmonary infections. None of the cases occurred among persons receiving prophylactic therapy with trimethoprim-sulfamethoxazole. Therapeutically, all patients appeared to respond well to standard antilegionella therapy or high doses of trimethoprim-sulfamethoxazole. Overall, these seven patients represent 1.7% of the patients with late-stage HIV infection (Walter Reed stage 5 or 6) in this cohort. L. pneumophila, although remaining an uncommon pathogen for HIV-infected patients, may produce serious disease in this population. HIV-infected persons should be considered at risk for legionnaires' disease, particularly in institutions where potable water supplies have become contaminated.