Seventy-five morbidly obese patients underwent jejunoileal bypass between December 1968 and October 1975. The average weight of 45 patients who had had the bypasses for over two years stabilized at 62.4% of the maximum preoperative value. Postoperative complications included recurrent diarrhea in 11% (8/74) and serum electrolyte deficits in 64% (48/75), most of which were transient. Potassium and calcium deficiencies were usually correctable by oral supplementation, but hypomagnesemia persisted in 23% (16/71) despite supplementation. Nine percent (4/43) had biopsy-proved hepatic cirrhosis after one year. Other complications were polyarthralgia, bone demineralization, renal stones, and vasculitis. Three patients required reanastomosis to original bowel continuity; all rapidly regained weight. One died of vasculitis and hepatic failure attributable to the bypass. Jejunoileal bypass is suitable only in morbidly obese patients with particularly high motivation, whose risk factors outweigh those risks incurred through bypass.