Between October 1967 and November 1977, the jejunoileal bypass was performed on 177 patients for morbid exogenous obesity. The female--male ratio was 9:1. The mean follow-up period was 3.4 years and their ages ranged from 15 to 58 years. Eighty-five per cent of this patient population base were between the ages of 21 and 49 years, and in 83% the onset of obesity was in childhood. Four parameters were used to assess the effectiveness of this procedure: 1) the ponderal index, 2) the per cent of ideal weight, 3) complications, and 4) diarrhea. Using the ponderal index, 38% of the results were excellent, 20% satisfactory, and 25% poor. When the per cent of ideal weight was used, the results were 24, 27 and 32% respectively. For complications, the results were 55, 23 and 5% and with diarrhea, 53, 22 and 8%. A summary of these mean values was 42.5, 23 and 17.5% for excellent, satisfactory and poor results. There were four deaths in this series, occurring 2--16 months postoperatively, due to sepsis, pulmonary embolism, drug overdose, and liver failure. Of the 28 patients (17%) requiring revision, eight were revised for inadequate weight loss, four for excessive weight loss, 15 for uncontrollable diarrhea, and 11 for metabolic electrolyte problems. In 14% the revision was required for multiple indications. A review of 100 of these patients to determine their response to the procedure revealed that 91% were able to recommend the procedure to other patients and intrepreted their results as being excellent in 51%, good in 36% and fair in 11%. Continued use of this procedure should be deferred pending much needed investigation of the associated complications.