We reviewed the records of 44 patients with AIDS who had 45 episodes of severe Pneumocystis carinii pneumonia (PCP). While 9 patients required intubation and mechanical ventilation (MV) on admission, continuous positive airway pressure (CPAP) by face mask was the initial measure in 36 episodes. There were 25 patients managed with CPAP alone, 23 of whom survived. Among the reasons for delayed intubation and MV (11 patients) was that treatment failure was strongly associated with non-survival, since all 6 such patients died. The in-hospital mortality for severe PCP in this study was 33% overall, and reached 65% for mechanically ventilated patients. The 1-year survival was 43% (95% confidence interval, 28%-58%). These data confirm the improved prognosis for patients with AIDS and severe PCP, and suggest that mask CPAP may be an adequate mean of ventilatory support in this setting.