Unilateral reexpansion pulmonary edema (RPE) is a rare complication of the treatment of lung collapse secondary to pneumothorax, pleural effusion, or atelectasis. Although RPE generally is believed to occur only when a chronically collapsed lung is rapidly reexpanded by evacuation of large amounts of air or fluid, in this review 15 of 47 cases of RPE available for assessment occurred when the pulmonary collapse was of short duration or when the lung was reexpanded without suction. The pathogenesis of RPE is unknown and is probably multifactorial. Implicated in the etiological process of RPE are chronicity of collapse, technique of reexpansion, increased pulmonary vascular permeability, airway obstruction, loss of surfactant, and pulmonary artery pressure changes. Since the outcome of RPE was fatal in 11 of 53 cases reviewed (20%), physicians treating lung collapse must be aware of the possible causes and endeavor to prevent the occurrence of this complication.