Gastrointestinal duplications are rare congenital lesions that can develop anywhere along the alimentary tract and may present in the newborn period as an abdominal mass. They are differentiated from other intraabdominal cystic lesions by the presence of a normal gastrointestinal mucosal lining. Multiple theories have been proposed to account for these lesions; however, no single theory adequately explains all the known duplications. They are most frequently single, tubular, or cystic and located on the mesenteric side of the native alimentary tract structure. Symptoms often are related to the location of the duplication; oral and esophageal lesions can create respiratory difficulties, whereas lower gastrointestinal lesions may cause nausea, vomiting, bleeding, perforation, or obstruction. Treatment is resection with care taken to protect the common blood supply of the native structures. Occasionally, a partial resection with mucosal excision is required to preserve intestinal mucosa.