The mortality rate among patients with human immunodeficiency virus (HIV) requiring mechanical ventilation (MV) for acute respiratory failure (ARF) secondary to Pneumocystis carinii pneumonia (PCP) is still a matter of discussion. For some authors, it is in the 50 percent range, while for others the prognosis is grim, with virtually no survivors. The aim of this retrospective study conducted between January 1987 and January 1992 was to analyze the outcome of such patients. We studied 33 patients, 29 men and 4 women (38.6 +/- 9.9 years, 21 homosexuals, 8 intravenous drug users, 3 transfusion related, 1 heterosexual) infected by HIV for at least 19.7 +/- 21.6 months. It was the first PCP episode in all but 2 patients and the diagnosis was made by bronchoalveolar lavage (n = 32) or lung biopsy specimen (n = 1). Only three patients were receiving primary prophylaxis for PCP (trimethoprim-sulfamethoxazole [TMP-SMZ], n = 2; pentamidine, n = 1). Pneumocystis carinii pneumonia was the first manifestation of AIDS in nine patients. The duration of symptoms prior to treatment was 19.6 +/- 11.3 days. At the time of hospital admission, laboratory findings were as follows: PaO2 = 40.7 +/- 7.8 mm Hg on room air; serum LDH = 1,172 +/- 792 IU/L; T4 cell count = 60.2 +/- 67/mm3. Mechanical ventilation was always required for ARF, which was never induced by bronchoscopy. The interval between treatment and MV was 8.1 +/- 6.5 days and the duration of MV was 11.4 +/- 9.9 days. The patients were classified into 3 groups on the basis of the duration and type of treatment before MV, as follows: group 1, n = 10: TMP-SMZ (20-100 mg/kg) IV and methylprednisolone (MP) < 5 days before MV; group 2, n = 4: TMP-SMZ > or = 5 days and MP < 5 days; group 3, n = 19: TMP-SMZ and MP > or = 5 days before MV. (The MP dose was as follows: 240 mg/d once a day from day 1 to day 3; 120 mg/d from day 4 to day 6; and 60 mg/d from day 7 to day 9.) Despite MV, TMP-SMZ, and MP, death secondary to PCP-related ARF occurred in 81.9 percent of patients, 20 +/- 4.8 days after the beginning of treatment and 11.4 +/- 9.9 days after the beginning of MV. Six patients survived, five in group 1 and one in group 3.(ABSTRACT TRUNCATED AT 400 WORDS)