BACKGROUND: A prospective, randomized trial comparing vertical banded gastroplasty (VBG) and gastric bypass (GB) was performed on 106 patients between 1987 and 1990. METHODS AND RESULTS: Failures of these two operations (manifested by failure to lose weight, late weight gain or intolerance of adequate oral intake) were treated by means of a third operation, isolated gastric bypass (IGB), in which the small gastric pouch was isolated from the gastric fundus. The latter operation was significantly better than VBG or GB and achieved a 63% success rate, i.e. body mass index (BMI) < 35 kg m(2) and less than 50% excess weight. During the year following this trial an additional 54 patients underwent IGB. When this operation was performed for morbid obesity and was the Initial procedure, 96% of the patients achieved a successful result. If IGB was performed as a revision procedure or for super obesity (BMI > 50 kg m(2)), the success rate was 63% with 100% follow-up at 40 months. Major morbidity occurred in six of the 160 patients who underwent 195 operations (the trial period and subsequent year). There were no deaths and follow-up was 98%. CONCLUSIONS: The ideal gastric operation based on this study emphasizes the following requirements: a small pouch (< 15 ml) totally separated from the stomach, a pouch not dependent on staples, placed in the dependent position to prevent stasis, constructed without foreign material and with an anastomosis which permits ingestion of solid food.