Background. Removal of the right middle and lower lobes often leaves a pleural space problem that can cause prolonged air leaks. Methods. A single surgeon prospectively randomized 16 patients who underwent bilobectomy. Eight patients had 1200 mL of air injected under the right hemidiaphragm after bilobectomy and 8 did not. The air was injected through a small transdiaphragmatic opening made in the right hemidiaphragm at the time of pulmonary resection. Results. The age of the patients, preoperative pulmonary function, preoperative comorbidities, indications for surgery, and final pathology were not significantly different between the two groups. On postoperative day 1, a pneumothorax was present in 1 patient (13%) in the pneumoperitoneum group (P group) and in 4 patients (50%) in the nonpneumoperitoneum group (N-P group). On postoperative day 1, an air leak was present in 1 patient (13%) in the P group and 5 patients (63%) in the N-P group (p < 0.001). By the third postoperative day, no patient in the P group had an air leak; however, a leak was present in 4 patients (50%) in the N-P group (p < 0.001). Median hospital stay in the P group was 4 days (range, 3 to 6 days), compared with 6 days (range, 4 to 8 days) in the N-P group (p < 0.001). Three patients in the N-P group were sent home with a Heimlich valve. There was no operative mortality and no complications from the pneumoperitoneum. Conclusions. We conclude that pneumoperitoneum after bilobectomy is safe and easy to do. It decreases the incidence of air leaks and of pneumothoraces and shortens hospital stay without increasing morbidity. We recommend pneumoperitoneum after bilobectomy at the time of thoracotomy, especially if there are residual small air leaks that cannot be sealed before chest closure. (C) 2000 by The Society of Thoracic Surgeons.