We conducted a case-control study to determine the incidence and clinical features of and risk factors for Pseudomonas aeruginosa infections in patients infected with human immunodeficiency virus (HIV). Twenty-five patients who had 37 episodes of P. aeruginosa infection from 1990 through 1992 were identified. Most of the patients (92%) were homosexual men with low CD4+ lymphocyte counts and a history of AIDS. The annual incidence rates of P. aeruginosa infection were 3.5% (1990), 6.3% (1991), and 8.7% (1992). Most infections were community-acquired (68%) and involved the respiratory tract (73%). Patients were more likely than HIV-infected controls to have AIDS and had more AIDS-defining opportunistic illnesses. The overall mortality was 36%. Recurrent episodes were common (39%). We conclude that P. aeruginosa infections may be an increasing problem in patients with extremely advanced HIV infection. Clinicians should consider including antibiotics with activity against P. aeruginosa in the empirical treatment for suspected bacterial infection in patients with advanced HIV infection.