This paper is to present 7 cases of unilateral pulmonary edema occurred after thoracotomy in 44 cases of the spontaneous pneumothorax. 1. 4 cases of unilateral pulmonary edema were found in male and the remainder in female. The age range of the patients in the series was 21-60 years, and most frequently in the 3rd and 4th decade. 2. The unilateral pulmonary edema was usually absorbed within 10 days. 3. The unilateral pulmonary edema was more frequently occurred in patients who had long history of pulmonary collapse and rapid and complete re-expansion of the collapsed lung. 4. The mechanism of the unilateral pulmonary edema following rapid re-expansion of the spontaneous pneumothorax by thoracotomy were reviewed in the recently published literatures.