Intraoperative lobar torsion occurred in 4 of about 2000 patients subjected to thoracotomy. Two of the patients died. Early diagnosis and proper management are of great importance to the outcome. Temporary deflation of the diseased lung by using double lumen endobronchial tube is a potential risk. Early progressive lobar opacity without signs of atelectasis on conventional chest radiograph is indicative of this serious complication. Computerized tomography and bronchoscopy are of diagnostic value. Exploratory thoracotomy must be performed without delay. The injured parenchyma should be sacrificed unless the diagnosis is obtained very early. When the injured lobe or lung is rotated back into normal position the airways may be flooded with serosanguinous fluid which promptly has to be removed. If an attempt is made to save the lobe or the lung, tracheostomy for frequent suction of the airways is indicated in order to prevent "spill-over" and dangerous postoperative hypoxia.