The epidemiology and etiology of spontaneous pneumothorax (SP) are shifting away from the predominance of subpleural bleb disease as emphasized by most reports since that of Kjaergaard (Sweden, 1932). We conducted a retrospective review of all patients admitted to a large urban hospital with the diagnosis of SP over the past 8 years. Of 120 patients, 32 had the acquired immunodeficiency syndrome (AIDS) (group 1, 26.6%), 43 patients had classic subpleural bleb disease or chronic obstructive pulmonary disease with blebs (group 2, 35.8%), and 45 patients had nonbleb disease exclusive of AIDS (group 3, 37.5%). These three groups were studied with respect to primary success rates with differing modalities of therapy. Bilateral SP occurred in 34% of group 1 patients, 2% of group 2 patients, and 11% of group 3 patients. The in-hospital mortality was 34% in group 1 compared with 2% in group 2 and 4% in group 3. Thirty-four percent of group 1 patients had recurrent SP compared with 16% of group 2 patients and 8% of group 3 patients. This report describes the changing etiology and epidemiology of SP in a large urban hospital from 1983 to 1991 and represents the largest single-institution report of AIDS-related pneumothorax. Standardized therapy was shown to have predictably favorable results in patients with bleb disease and nonbleb disease exclusive of AIDS. SP in patients with AIDS was associated with a high mortality rate and primary treatment failure; small-bore catheters and nondrainage therapies have a very limited role in these patients.