Since 1962, jejunoileal bypass has been performed on 59 male and 171 female subjects, aged 18-55 yr; these patients were followed clinically. Postoperative wt loss at 2 yr averaged 37% in men and 35% in women. Hypokalemia (23%), hypocalcemia (22%), hypoalbuminemia (9%), metabolic acidosis (14%), elevated liver enzyme values (41%) and hyperbilirubinemia (6%), were the most commonly encountered blood chemical alterations. Complications were arthritis syndrome (men, 8%; women, 19%), urinary calculi (men, 24%; women, 10%), cholelithiasis (men, 10%; women, 9%), liver impairment (men, 2%; women, 6%) and major emotional upset (men, 8%; women, 9%). Of the patients, 49% of the men and 51% of the women required rehospitalization for management of complications, surgery for hernia, anorectal disorders, nutritional support and metabolic study. There were 19 bypass-related deaths (8%), including 10 due to liver failure.