Background: Enteric duplication cysts (CDE) are rare congenital malformations of the gastrointestinal tract. They may be cystic or tubular in conformation. Histologically they resemble the general structure of digestive tub: have a well-developed coat of smooth muscle and an epithelial lining that represents some portion of the intestinal tract mucosa and contain various concentrations of mucus. Retroperitoneal localization of CDE is quite rare, usually reported by an ultrasound investigation in the pre- or perinatal period. The small intestine is the most common location and retroperitoneum is an extremely rare site, especially difficult to be diagnosed in the adulthood. Material and methods: Herein, we report a case of a retroperitoneal CDE. A 17-year-old woman visited our institution because of an abdominal mass detected on abdominal ultrasound. The presumptive diagnosis: lymphangioma. Results: The patient presented at our emergency department with pain in the left hipocondrium, which appeared in the last 3 month. Blood cell count, urine and serum analysis without abnormalities. USG and multiphase abdominal CT diagnosis sound as retroperitoneal lymphangioma, but morphological assays revealed a CDE. Conclusions: Enteric duplication cysts are rare congenital enteric malformations with a cystic appearance. Its diagnosis represents a challenge for clinicians. Only histological examination can prove a real enteric cyst.