Gastric bypass is an effective treatment for morbid obesity. However, it is sometimes complicated by stenosis or ulceration of the gastrojejunal anastomosis. Stomal ulceration and stenosis developed in, respectively, 12.5% and 12% of 191 patients who underwent gastric bypass. Only 3% had both complications simultaneously. The risk of developing either complication was highest in the first 2 months after surgery. Stomal stenosis responded to endoscopic dilation in all instances, and appears to be a safe and effective method of treating this problem following gastric bypass. Stomal ulceration healed with an H2 blocker and sucralfate administration in all but one patient. Postoperative weight loss was similar in patients with or without stomal stenosis or ulceration. We conclude that, although stomal complications occur in about 20% of all patients undergoing gastric bypass, they can almost always be managed by conservative therapy.