A case of pulmonary edema following reexpansion of a collapsed lung due to pneumothorax is described and illustrated. The importance of recognizing this relatively uncommon phenomenon is stressed. The development of such edema can be prevented by avoiding application of sudden and excessive negative pleural pressures during the evacuation of a pneumothorax or a pleural effusion. The edema generally occurs in a lung that has been collapsed for more than three days. The importance of the duration of pulmonary collapse in the causation of edema is demonstrated in this patient.