Sixty-six patients who had a jejunoileal bypass with ileosigmoidostomy for intractable obesity were reviewed. Thirty-three patients had sudden, severe, upper pain develop in the abdomen with distention from one to four years after the original operation. All 33 patients had a repeat laparotomy from one to six years after the initial bypass procedure. In every instance, a dilated, hypertrophied defunctioned ileum was found proximal to the ileosigmoidostomy. In 11 patients, an ileosigmoid volvulus was present. In every instance, the ileosigmoid anastomosis was dismantled and an end-to-side ileotransversostomy performed. In one patient, an ileal volvulus developed proximal to the ileotransversostomy because of an inadvertent technicality and this was corrected by reoperation. The remaining 32 patients have been asymptomatic since the ileosigmoidostomy was converted to ileotransversostomy. To date, in more than 200 primary operations for morbid obesity, the ileum has been drained into the transverse colon. None of these patients have had obstruction of the defunctioned small bowel develop.