Fifteen patients with AIDS were hospitalized on the pulmonary service during the period from 1981 to 1983. We were impressed with the frequency and severity of lung involvement in these patients and evaluated them with respect to their pulmonary manifestations of AIDS. The 13 men and two women had a mean age of 32 years. Ten were active intravenous drug abusers with a mean drug use of 8.1 years. All presented with profound weight loss, ten with nonproductive cough, and eight with significant dyspnea. Fourteen of 15 patients had Pneumocystis carinii pneumonia (PCP) at the time of our evaluation. Chest radiographs in these 14 patients showed no uniform pattern which was predictive of PCP. However, all 13 patients tested had a widened alveolar arterial oxygen gradient (mean: 59 mm Hg) which correlated well with the presence of PCP. The most common pulmonary finding in our AIDS patients was infection: 14 had PCP which was readily diagnosed by transbronchial lung biopsy in eight patients, and five patients were found to have disseminated Mycobacterium avium-intracellulare which often developed after "recovery" from PCP. Therapy for PCP with trimethoprim/sulfamethoxazole (TMP/SMZ) was unsuccessful in eight of ten patients; four of these eight TMP/SMZ failures responded to pentamidine. Mortality was 100 percent in patients who had AIDS for more than one year, and 70 percent in those less than one year. Despite some symptomatic responses to therapy for pulmonary infections, the mortality in AIDS seems to be unaffected by appropriate therapy for the pulmonary manifestations of this disease.