PURPOSE: Gastroesophageal reflux in infant is a physiological process. However, surgery is performed in high risk infants with severe gastroesophageal reflux disease (GERD) when medical management fails. This study focuses on efficacy and safety of Nissen fundoplication for GERD in infants under age 12 months. METHODS: This study was a retrospective case analysis of 11 neonates and infants under 12 months of age who underwent Nissen fundoplication following a failure of medical treatment between June 2010 and June 2013 at Pusan National University Children's Hospital. The records were reviewed to determine the effect of fundoplication on symptoms and post-operative complications. RESULTS: A total of 11 infants consist of four males and seven females. Mean birth weight was 2,305.5+/-558.6 g (1,390-3,130 g). They had some underlying disease, which are not related with GERD such as congenital heart disease (54.5%), prematurity (45.5%), neurologic disease (18.2%), respiratory disease (18.2%), and other gastrointestinal disease. Mean body weight at surgery was 3,803.6+/-1,864.9 g (1,938.7-5,668.5 g). Mean age at operation was 99.9+/-107.6 days (17-276 days). Duration from operation to full enteral feeding was 10.9 days. Symptoms related GERD disappeared in all patients including one who got reoperation. One infant died of congenital heart disease unrelated to surgery. There were no complications related to fundoplication. CONCLUSION: Fundoplication is effective and safe treatment in the neonates and infants with severe GERD.