A rare case of gastric duplication of childhood is reported. A 1-month-old boy underwent pyloromyotomy for infantile hypertrophic pyloric stenosis. At laparotomy, a protruding lesion was identified in the anterior wall of the pylorus. The pylorus was hypertrophic as indicated preoperatively, and a normal pyloromyotomy was performed. Wedge biopsy of the protruding lesion revealed an intestinal structure, and gastric duplication was diagnosed. The child remained asymptomatic thereafter, but considering the risk of the duplication becoming symptomatic, a second laparotomy was performed at 1 year of age. The duplication cyst shared part of the wall with the pylorus, and the cyst was removed by cystectomy, leaving the pyloric muscle intact. The cyst was found to be communicating with the pancreatic duct. The child is doing well without any symptoms as of 18 months after second laparotomy. To the best of our knowledge, this is the youngest case of gastroduodenal duplication with pancreatic duct communication yet reported.