One hundred and one patients underwent jejunoileal bypass after careful preoperative evaluation. These patients were re-evaluated after operation on a frequent basis, and 23% have required restoration of intestinal continuity (reanastomosis) by a mean postoperative time of 44 months. The most frequent reasons for reanastomosis were liver dysfunction (5% of the entire series), severe malnutrition or weakness (5%), and late electrolyte imbalance (4%). Two patients did not survive reanastomosis, both having liver failure. Of the patients who did survive, weight gain (approaching prebypass weight) and improvement in liver function tests, electrolyte balance, serum vitamin levels, and diarrhea have been the rule. Of the entire series of 101 patients who underwent bypass, 58% either had life-threatening complications, had to be reanastomosed, or died. These morbidity and mortality rates raise the important question of whether jejunoileal bypass is an appropriate procedure for the treatment of morbid obesity.