Spontaneous pneumothorax is usually seen in young adult male. And typically, the patient is a tall, thin, 20- to 30-year-old male. Usually the pneumothorax results from rupture of a pulmonary bleb. Author reviewed 66 cases of spontaneous pneumothorax experienced in the Dept. of Thoracic & Cardiovascular Surgery, Pusan National University Hospital, since Jan., 1980 to Aug., 1986. The clinical data were summarized as follows: 1. The age distribution of spontaneous pneumothorax: 17 to 34 years old and mean age was 25.3 years. 2. The sex distribution of spontaneous pneumothorax: 52 in men, 14 in women and the ratio was 3.7:1. 3. Chest dimension in male patients: Maximum posteroanterior distance [MPA], MPA/Maximum width [MW]: Significantly smaller than control group. Distance from second to tenth rib on left [L2-10], Distance from second rib on right to diaphragm [R2-D], R2-D/MW: Significantly larger than control group. 4. Chest dimension in female patients: MPA, MW: Significantly smaller than control group. Distance from second rib on left to diaphragm [L2-D], Distance from second to tenth rib on right [R2-10], R2-D, L2-10/MW, L2-D/MW, R2-10/MW, R2-D/MW: Significantly larger than control group.