We observed 56 cases of nontraumatic pneumothorax clinically and statistically, which had been experienced at the deparment of chest surgery. St. Mary`s Hospital,Catholic Medical College in theserecent years. 1] In the underlying pathology of spontaneous pneumothorax, nontuberculous origin [60.7%], especially due to pulmonary emphysema or blebs[17.8%], especially due to pulmonary emphysema or blebs[17. 8%], tended to increase as the reports of foreign countries, but tuberculous origin was still high in our country[39.3%]. Considering the 14 cases, unknown underlying pathology, the most of them might have scattered blebs which were not revealed in chest Roentgen films. 2] The principle treatment done in our clinic was as follows; The patients, below 20% lung collapse were treated by bed rest and abdominal respiration. The patients, between 20% and 40% lung collapse were treated by repeated pleural aspiration or closed thoracotomy followed. The cases,over 40% lung collapse were treated by closed thoracotomy initially. 3] The average duration of indweIling catheter was 3 to 4 days in the closed thoracotomy. We used to not remove the indwelling catheter early to promote pleural adhesion. 4] Sometimes, the closed thoracotomy drainage induces bronchial irritation and asthmatic attacks, especially in old age group accompanying pulmonary emphysema. In these cases, respiratory difficulties and acidosis should be prevented and controlled with medical treatment including steroid therapy.[KTCS 1969;1:133-140]