We present a rare case of gastric duplication cyst that was suspected prenatally. A routine prenatal ultrasonography (US) showed an abdominal cyst with peristalsis and a provisional diagnosis of enteric duplication was made. A healthy male infant was born at 39 weeks gestation and postnatal US identified a cyst, 5x3x2 cm in size, adjacent to the pancreas. At laparotomy, a cyst was found located in the lesser sac, but completely separated from the stomach, and partially adhered to the body of the pancreas and the crura of the diaphragm. Total excision of the cyst was successful. Histopathologic examination confirmed that the cyst wall consisted solely of normal gastric tissue with erosions. To the best of our knowledge, this is the first report of an isolated gastric duplication cyst that was detected prenatally and resected during the neonatal period.