A prospective study was conducted in the emergency setting to determine the efficacy of treatment of simple pneumothorax by catheter aspiration. Patients who were successfully treated were discharged to home. Sixty-one patients with a total of 76 pneumothoraces were involved in the study. The overall success rate was 75.6%, with an 82% success rate for needle-induced, 75% for traumatic, and 45% for spontaneous pneumothorax. The duration of symptoms, the size of the pneumothorax, the patient's age, and a prior history of pneumothorax did not affect the outcome. The poorest results were noted with spontaneous pneumothoraces, as would be expected since a majority of these patients have preexistent lung disease. Catheter aspiration of simple pneumothorax offers a cost-effective approach to this clinical problem.