Pulmonary barotrauma developed in 18/430 patients receiving respirator support for longer than 12 hours. Pneumothorax occurred in 15 of these patients and was treated with tube thoracostomy and 15-20 cm H2O pleural suction. Full reexpansion of the lungs were achieved in all but three patients, two of whom had bronchopleural fistulae. Major complications occurred in 8/15 patients developing pneumothorax. We recommend extreme conservatism in clamping or removing tube thoracostomy. There should be no air leak and full lung expansion for 48 hours, followed by a trial of underwater seal drainage without recurrence of pneumothorax. Removal should be preceded by an additional trial of tube clamping.