Objective To complete a long-term (>5 years) follow-up of patients undergoing isolated gastric bypass for severe obesity. Summary Background Data Previous experience as well as randomized trials suggested that the ideal operation for obesity should rely on manipulation of satiety rather than the production of malabsorption. Such an operation should incorporate a small gastric pouch of less than 30 mL placed in a dependent position on the lesser curvature of the stomach, not dependent on staples, and separated from the remaining stomach with a retrocolic, retrogastric Roux-en-Y gastrojejunostomy without external support. Methods The authors established an obesity clinic where patients were seen six times during the first year and semiannually thereafter. Emphasis was placed on defining success in terms of approximation to normal body-mass index. Results Of 274 patients, 243 (89%) were followed up for 5.5 ± 1.5 years. Before surgery, the patients were obese (n = 13), morbidly obese (n = 134), or super-obese (n = 96). The obese and morbidly obese group achieved an excellent result, and the super-obese a good result. Individual results showed considerable variation from the mean. Conclusions This study of isolated gastric bypass with a 5.5-year follow-up rate of 88.6% revealed a success rate of 93% in obese or morbidly obese patients and 57% in super-obese patients. Isolated gastric bypass compares favorably with biliopancreatic diversion in terms of weight loss, maximum weight loss, weight regain, current body-mass index, and percentage of patients with a body-mass index less than 35 kg/m2.