Severe acute respiratory syndrome (SARS) presents an unprecedented diagnostic and therapeutic challenge to clinicians. Despite recent progress in identifying and analyzing the coronavirus that is responsible for it, few reports have addressed the clinical complications of SARS. The present study was a two-center retrospective cohort study. All patients in the study had SARS, were managed in the two major Hong Kong hospitals (ie, Prince of Wales Hospital and United Christian Hospital), and had developed spontaneous pneumothorax during their hospitalization between March 10, 2003, and April 28, 2003. Spontaneous pneumothorax was reported in 6 of 356 SARS patients who were treated at the two hospitals during the period. This represents an incidence of 1.7%. None of the six patients had a history of smoking or pulmonary disease. The rate of admission to the ICU was 66.7% and the crude mortality rate was 33.3% in this group of patients. There was a trend for the mean neutrophil count in these patients to be higher than in previously reported cohorts of comparable SARS patients (14.5 x 10(9) vs 4.6 x 10(9) neutrophils per liter, respectively). Conservative measures like tube thoracostomy or observation alone offered satisfactory initial symptomatic management in five of six patients. Spontaneous pneumothorax is a specific and potentially life-threatening complication in SARS patients. Patients with extensive lung injury, as indicated by severe clinical courses, and in particular high neutrophil counts, appear to be most at risk. The benefits of surgical management must be balanced against the potential risks to health-care workers.