Since Frankel reported the congenital anomalous intestinal duplication incidentally during autopsy in 1883, about 228 cases has been reported on the literatures. In our severance hospital, one case of ileal duplication was found, and was confirmed by pathology and surgery. This patient of duplication usually reveals the symptoms of abnormal distension, pain and palpable abdominal mass, and sometimes the symptoms of intestinal obstruction. On x-ray flate abdomen, huge occupying mass displaces intestinal gas pattern to left side. Barium enema study reveals elongation and displacement of ileum by large extrinsic mass. And cecum is also displaced upward. On the IVP, this extrinsic mass is not related to kidneys. Also, the literature was reviewed.