Conversion of jejunoileal bypass to gastric bypass was performed in 11 patients because of metabolic problems and physical discomforts, and in three patients because of insufficient weight loss. There was no mortality and little morbidity after operation. An additional mean weight loss of 6% occurred, and weight stabilized satisfactorily in most patients. Two patients regained significant weight. Serum cholesterol levels rose within a month in most patients, with a mean increase of 61%. However, levels remained within normal limits. Serum triglyceride levels did not change significantly, especially in patients whose weight remained stabilized. Plasma glucose levels remained normal in all patients, including four patients who had been clinically diabetic before jejunoileal bypass. These patients had become normoglycemic immediately after jejunoileal bypass, and remained normal after conversion to gastric bypass.