Spontaneous pneumothorax is the sudden collapse of a lung usually caused by air leaking from a sub-visceral pleural bleb. Response to closed thoracotomy, needle aspiration and simple observation is usually prompt and effective. But in some cases, these are unsuccessful and open thoracotomy is indicated. Author reviewed 37 cases of open thoracotomy in spontaneous pneumothorax experienced in the Dept. of Thoracic and Cardiovascular Surgery, Pusan National University Hospital, since Jan., 1980 to Dec., 1984. The results were as follows: 1. The causes of spontaneous pneumothorax: 73.0% was primary, 27.0% was secondary origin. 2. The most frequent age group of the patient: Between 11 and 30 years old. 3. All of te patient were male. 4. The side of open thoracotomy: 58.8% was right side, 8.8% was both side. 5. The most common indication of open thoracotomy; Persistent air leakage. 6. The most frequent sites of bleb or bullae: A-P segment in the L.U.L. and apical segment in the R.U.L.