To examine intensive care unit (ICU) admission rates and diagnoses of patients with HIV infection, and to determine the outcomes of different critical illnesses, we analyzed data derived from the 63 patients who were admitted to an ICU from among the 1,130 adults with HIV infection who did not have AIDS at the time of enrollment in a multicenter prospective study. Patients were admitted and treated according to the judgment of their physicians. During 4,298 patient-years of follow-up for the entire cohort, there were 1,320 hospital admissions, of which 68 (5%) included admission to an ICU. Twenty-five (40%) of the patients admitted to the ICU died during that admission. Twenty-four patients (38%) were admitted with a principal diagnosis of lung disease; 11 had Pneumocystis carinii pneumonia (PCP), one of whom was coinfected with Aspergillus fumigatus and Legionella pneumophilia, and six of them (55%) died. Four had bacterial pneumonia, two had pulmonary edema caused by renal failure, and one each had pulmonary tuberculosis, pulmonary Kaposi's sarcoma, pneumothorax, adult respiratory distress syndrome, severe pulmonary fibrosis, cytomegalovirus pneumonitis, and metastatic adenocarcinoma to the lungs. Eleven of these 14 patients (79%) died. Thirty-nine patients had 44 admissions for nonpulmonary diagnoses, including gastrointestinal disorders (14 admissions), cardiovascular disorders (nine), sepsis syndrome (six), neurologic disorders (four), monitoring and ICU nursing care during or after a procedure (four), metabolic disorders (three), trauma (two), drug overdose (one), and unknown reasons (one). Nine (23%) of these patients died. Twenty-eight patients underwent mechanical ventilation, and 16 (57%) died. Seven (25%) had PCP (five died), seven had other primary pulmonary diseases (six died), and 14 were placed on mechanical ventilation for nonpulmonary disorders (five died). Survival did not correlate with CD4 count determined within 6 mo of admission to the ICU. In conclusion, the range of indications for critical care in patients with HIV infection is diverse. PCP accounted for only 16% of the ICU admissions, and mechanical ventilation for PCP and other pulmonary disorders was associated with a high mortality rate. In contrast, mechanical ventilation for nonpulmonary disorders, and admission to the ICU for nonpulmonary diagnoses was associated with a more favorable outcome.