Between 1970 and 1975, 16 adolescent patients with a mean age of 17.8 years underwent jejunoileal bypass for exogenous morbid obesity. Their mean preoperative weight was 273.8 lbs. The total weight loss averaged 48 kg per patient. An extended evaluation process was instituted to determine the effectiveness of this procedure. Six of these parameters were the ponderal index (PI), body mass index, Broca's index, the per cent of ideal weight, complications, and diarrhea as a separate complication. A new formula was introduced to interpret weight loss as the percentage of excess pounds lost (PEPL). Three required reestablishment of normal intestinal continuity. There were no deaths in the group. Fifty and 69 per cent experienced excellent weight loss and postoperative PI respectively; excellent results were obtained in 27.5 per cent in both categories. In contrast, 50 per cent had a weight loss less than 100 lbs and 19 per cent a poor PI postoperatively; 13 per cent experienced poor results by both criteria. Linear growth in all patients continued along a normal curve, and their heights were above the mean.