OBJECTIVE Descriptive study of severe respiratory infections caused by Pseudomonas aeruginosa in patients with HIV infection. METHODS Review of clinical records of HIV-positive patients admitted in a tertiary hospital from 1-1-1990 to 9-30-1995. The patients included in this study were those with P. aeruginosa recovered from respiratory or blood samples and respiratory symptoms. RESULTS Forty patients suffered 77 episodes. The incidence in the HIV-positive admitted population during the study period was 2.6% but 3.2% in the last year. Ninety-seven percent of patients met criteria for AIDS. Twenty-eight patients (70%) had other bacterial infections. In 78% of patients no classical predisposing factor was found for this infection. Twenty-seven patients (67.5%) came regularly to the day hospital or had been previously admitted to the hospital (recent hospitalization). Twenty-five episodes (32.5%) were tracheo-bronchitis and 50 pneumonias (65%), of which 14 (28%) were cavitated and 7 (14%) bacteremic. Forty-nine percent of episodes were recurrences. Ten out of 15 tracheo-bronchitis in the first episode recurred; the new episode was more severe in 7 patients. Five patients received secondary prophylaxis after the second episode (4 with tobramycin in aerosol and 1 with colistin in aerosol). Two patients had recurrences after 86 and 62 days (mean: 74; SD: 12). Eight out of the 11 patients who did not receive prophylaxis (73%) had recurrence after a mean of 23 days (SD: 10) (p = 0.002). The mortality rate associated with P. aeruginosa was 22.5%. CONCLUSIONS The incidence of P. aeruginosa infections in our HIV-positive patients was 2.6% (3.2% in the last year). It is associated with severe immunosuppression and previous bacterial infection. The subacute involvement of the lower respiratory tract is most common. Over 50% of infections tend to recur more severely. The secondary prophylaxis increased the symptom-free period, although the number of patients who received it was small.