Reexpansion pulmonary edema is a rare complication of the treatment of lung collapse secondary to pneumothorax, pleural effusion, or atelectasis. But occasionally, severe morbidity and death may result. Reexpansion pulmonary edema occurs when chronically collapsed lung is rapidly reexpanded by evacuation of large amounts of air or fluid. In the treatment of the chronically collapsed lung, physicians must remember the possible events and prevent the complications. When the difference in airway resistance or lung compliance between the two lungs is exaggerated, conventional mechanical ventilation might lead to preferential ventilation with hyperexpansion of one lung and gradual collapse of the other. Differential ventilation has been advocated to avert this problem. By differential lung ventilation, we successfully treated a severe reexpansion pulmonary edema in two patients. Therefore we suggest that differential lung ventilation is the treatment of choice for severe reexpansion pulmonary edema.