From 1967 through 1974, a consecutive series of 35 patients with flail chest were treated with intermittent positive-pressure breathing (IPPB). The controlled ventilation contributed to stabilization of the thoracic cage in a favorable position for healing of the fractures. Surgical stabilization of the chest was not attempted in any of the cases. During treatment with IPPB, one patient died from profuse bleeding due to a generalized coagulation disorder, but the remaining 34 were discharged in a satisfactory respiratory condition. A late follow-up study of the pulmonary function one to eight years after the trauma included x-ray films of the trachea and lungs, kymographic studies of the diaphragm, spirometric and radiospirometric testing, and arterial blood gas levels. Eighteen patients were examined. Spirometric testing revealed astonishingly little impairment of the total pulmonary function. The radiospirometric studies with 133xenon showed a significant reduction of the regional perfusion only in five patients (2 to 4.5 pulmonary segments). Kymographic study of the diaphragm gave no further information and was less selective compared with the other tests of pulmonary function. Owing to the encouraging early and late results in this study, early treatment with IPPB is considered to be the method of choice in flail chest with paradoxic respiratory movements.