Enteric duplication cysts (EDCs) can occur in any portion of the alimentary tract, but are most commonly associated with the small bowel and esophagus. Retroperitoneal location is really unusual. This 19-year-old female was in excellent health, but a week's abdominal pain made her search for a doctor's help. After the detailed examination, surgical intervention was performed under the impression of cystic tumor of the retroperitoneum. A retroperitoneal cystic tumor, 13.0 x 8.0 x 3.5 cm in size, without any communication with the alimentary tract was noted during the operation. Finally, EDC was diagnosed after the pathologic examination of this resected cystic lesion. To our knowledge, there have been only 6 reported cases of EDC of the retroperitoneum in the English literature. This report concerns the seventh case of retroperitoneal EDC, in an adolescent, with different clinical presentation and histopathologic findings from the previous ones.