Nine children (age range, 5 weeks to 13 years) with gastroesophageal reflux unresponsive to medical management were evaluated with esophageal manometry studies before and after Nissen fundoplications were performed. All patients had a postoperative increase in lower esophageal sphincter (LES) pressure. The mean preoperative LES pressure was 11.3 mm Hg and the mean postoperative pressure was 22.3 mm Hg. The mean LES pressure increase after surgery was 10.9 mm Hg (range: 5.3 to 22.5 mm Hg). All patients ceased vomiting immediately after surgery and have gained weight at a rate greater than that expected for their age.