Background/Purpose: Gastroesophageal reflux (GER) is a common occurrence after repair of congenital esophageal atresia and is believed to be more frequent when the esophageal anastomosis is performed under tension. This study documents that esophageal anastomotic tension correlates directly with the severity of acid reflux into the esophagus in the rabbit model. Methods: Eight adult rabbits underwent complete esophageal transection with immediate reanastomosis (EA) and 12 underwent resection of a 1-cm segment of the midesophagus with reanastomosis under mild tension (EAT). Three-weeks postoperation continuous lower esophageal pH (LEpH) values were recorded for a 24-hour period for each rabbit, and compared with five normal unoperated rabbits. Results: The normal rabbit's average LEpH is 7.7. EA rabbits had LEpH values below 5.0 for a mean of 56 min/24 hr (3.8% of monitored time). EAT rabbits had LEpH values below 5.0 for a mean of 328 min/24 hr (25.5% of monitored time; P < .05). EA rabbits had a mean of 8.8 reflux episodes under 5.0 24 hr , whereas EAT rabbits had a mean of 29.6 reflux episodes under 5.0. All EAT rabbits had moderate to severe anastomotic strictures; no EA rabbits had strictures. There were no anastomotic leaks. Conclusions: Esophageal anastomosis with mild tension in the rabbit causes severe GER with resultant anastomotic strictures in almost all rabbits, in contrast to rabbits undergoing esophageal anastomosis without tension in whom strictures did not develop and had only small reduction in esophageal pH values.