The records of 80 patients with small intestinal duplication who presented to the department of pediatric surgery, Beijing Children's Hospital during a 25-year period were reviewed. According to the pattern in relation of the vascular supplies to the duplication and involved bowel, the duplications were classified into two types: parallel type (type I) and intramesenteric type (type II). In type I, the duplication was on the border of one leaf of mesentery and the straight artery of the duplication separated from the straight artery to the bowel. In type II, the duplication located in between the both leaves of the mesentery and the straight arteries passed over the both surfaces of the duplication to reach the bowel. It was found that of 83 duplications in 80 patients, 62 cases (75.4%) belonged to type I, and 21 (24.6%) belonged to type II. Surprisingly, 91.6% patients with type II associated with thoracic vertebral defects, whereas only 5.8% in type II had such defects. Results of this study suggest that the duplication of small intestines have relatively independent vascular supplies and could be resected without the adjacent bowel.