Pouch volume, stoma diameter, and pouch emptying rate were measured post-operatively and after 6 months in 45 morbidly obese patients who had been assigned to either horizontal gastroplasty (HGP) or vertical banded gastroplasty (VBGP) after pretreatment with diet alone. Pouch volume and stoma diameter were measured by a standardized radiographic method with blinded assessment by two observers. Pouch emptying rate was determined by a standardized scintigraphic method and expressed as the mean transit time (t₆₀). Pouch volume and stoma diameter did not change, whereas t₆₀ decreased by 36% during the first 6 months after HGP (p < 0.001). Pouch volume was larger after HGP (p < 0.001). Pouch emptying was faster after VBGP (p < 0.001), but these patients had the better weight loss (p < 0.001). Variation in weight loss after either operation was unrelated to pouch volume, stoma diameter, and t₆₀. Stoma diameter was not correlated with t₆₀. The study provides further evidence against the significance of stoma diameter and pouch emptying rate as determinants of weight loss after gastroplasty. The much smaller pouch volume after VBGP may favor weight loss.