Gastrointestinal tract duplications are uncommon congenital abnormalities. By definition, they are located in or adjacent to the wall of part of the gastrointestinal tract, have smooth muscle in their walls, and are lined by alimentary tract mucosa. The lining mucosa is not necessarily that of the adjacent segment of the gastrointestinal tract. The only clinically important ectopic tissues are gastric mucosa and pancreatic tissue. Although ectopic gastric mucosa is found in duplications at all levels of the gastrointestinal tract, it is most prevalent (43%) in esophageal duplications. Peptic ulcer within this ectopic tissue can account for unusual, often misleading symptoms. Ectopic pancreatic tissue is most common (37%) in gastric duplications and is associated with pancreatitis and elevated amylase levels. Detection of associated vertebral anomalies is a helpful clue in the radiographic diagnosis of duplications. Barium studies usually reveal an intraluminal, intramural, or extrinsic mass, and ultrasonography (US) demonstrates its cystic nature. When US findings are inconclusive, computed tomography can be used to show the true nature, location, and extent of the lesion, as well as associated vertebral anomalies and possible other duplications. Technetium-99m pertechnetate scintigraphy provides definitive evidence of a duplication when it contains ectopic gastric mucosa and is particularly useful for suspected esophageal, duodenal, and small bowel lesions.