Delayed gastric emptying in patients with gastroesophageal reflux disease may be due to an incompetent distal esophageal sphincter and/or a gastric abnormality. To determine the influence of the Nissen fundoplication on gastric emptying we studied the rate of gastric emptying before and after operation in 25 patients with proved gastroesophageal reflux disease. Nine patients had no gastric pathology, 9 had gastric acid hypersecretion, 5 had gastritis, and 2 had evidence of significant duodenogastric reflux. All were treated by Nissen fundoplication. Those with gastric acid hypersecretion also had a proximal gastric vagotomy (PGV) and the two patients with pathologic duodenogastric reflux were treated by a bile diversion procedure. We found that in gastroesophageal reflux disease with associated gastric pathology there was a higher prevalence of delayed gastric emptying before operation than in patients without gastric pathology. Nissen fundoplication was associated with speeding of gastric emptying in patients with or without gastric pathology. Proximal gastric vagotomy performed in association with Nissen fundoplication augmented the speeding of gastric emptying, which was advantagenous in most cases but detrimental in two. Every patient in whom gastric emptying was not normalized had postoperative symptoms. Only two of 20 patients with normal postoperative gastric emptying had postoperative symptoms. Both patients had preexisting gastric pathology. Based on these findings, the side effects associated with Nissen fundoplication are due to the failure to normalize gastric emptying rather than the operation.