The Pickwickian syndrome can be divided into two primary breathing disorders, which can affect patients alone or in combination: sleep apnea syndrome (SAS) and obesity hypoventilation syndrome (OHS). Between 1980 and 1990, 126 patients with respiratory insufficiency underwent gastric surgery for morbid obesity, 12.5% of the entire series. These patients weighed more (164 +/- 36 vs 135 +/- 25 kg, P less than 0.0001) and were more often men (62% vs 14%, P less than 0.001) than those without pulmonary dysfunction. Sixteen had OHS alone, 65 had SAS alone, and 45 had both. Of those with OHS, 38 have been followed for 5.8 +/- 2.4 y since surgery and 29 are currently asymptomatic. In the 12 patients in whom arterial blood gases were available greater than 5 y since surgery, the PaO2 increased from 54 +/- 10 to 68 +/- 20 mm Hg (P less than 0.0001) and PaCO2 fell from 53 +/- 9 to 47 +/- 11 mm Hg (P = 0.05). Of the 110 patients with SAS, 57 were available for follow-up an average of 4.5 +/- 2.3 y since surgery and 38 were completely asymptomatic, 15 had mild SAS, and 4 had both SAS and OHS. In 40 patients with pre- and post-weight reduction sleep polysomnograms, the sleep apnea index fell from 64 +/- 39 to 26 +/- 26 (P less than 0.0001). Although respiratory insufficiency of obesity patients had a higher operative mortality than did patients without pulmonary dysfunction (2.4% vs 0.2% after gastric bypass), weight loss was associated with significant improvements in sleep apnea, arterial blood gases, pulmonary hypertension, left ventricular dysfunction, lung volumes, and polycythemia.