A prospective randomized clinical trial was undertaken to compare the effects of gastric bypass with Roux-en-Y gastrojejunostomy and a gastric partitioning procedure. Operative groups were comparable, with regard to preoperative weight, age, sex, historic findings and operative complications. Post-operative weight loss was followed for one year. Patients receiving the gastric partitioning procedure showed significantly poorer weight loss as early as three months postoperatively than did those receiving gastric bypass. This poorer performance persisted throughout the study period.