Unilateral paralysis of the diaphragm due to nonmalignant disease is an uncommon disorder previously thought to have benign implications. Some patients, however, experience dyspnea and orthopnea with impairment of pulmonary function. Unilateral diaphragmatic plication was performed on 17 patients (16 men and 1 woman with a mean age of 53.7 years [range, 28 to 74 years]) during the last 10 years. Preoperatively each patient was shown to have paradoxical movement of the paralyzed diaphragm on sniffing and to have a reduction in forced vital capacity and lung volumes. These reductions were greater when the patient was in the supine position. All patients had moderate hypoxemia (mean arterial oxygen tension, 73.1 +/- 10.9 mm Hg). Plication was performed by imbricating the diaphragm in layers through a thoracotomy incision. After plication, all patients showed both subjective and objective improvement. Six patients were reassessed 5 or more years after plication (range, 5 to 7 years), and the improvement was maintained. Diaphragmatic plication is a safe and effective procedure for adult patients with dyspnea due to unilateral diaphragmatic paralysis; furthermore, the initial improvement is maintained.