In 57 consecutive morbidly obese patients randomized to gastric bypass (29) or gastroplasty (28) the stoma size was measured by a simple and reproducible endoscopical method at 2, 6 and 12 months postoperatively. The stomata enlarged with time but no difference in stoma size between the groups was observed. With gastroplasty at each measurement an increasing correlation, at one year statistically significant, was found between weight loss and stoma size. Gastroplasty patients with smaller stomata lost more weight than those with larger stomata. After gastric bypass no such correlation appeared but these patients lost more weight (42.3 kg versus 29.9 kg, p less than 0.001). This suggest that some additional factor regulating weight loss other than stoma size is at work in this method.