Cystic lymphangioma is a benign tumour that occurs secondary to obstruction of lymphatic channels. Its appearance in the paediatric age group is quite common, but adulthood presentation is infrequent. Common locations are head and neck areas, whereas intra-abdominal occurrence is rare. To date, a few retroperitoneal cystic lymphangioma cases have been reported. A pre-operative clinical detection is always confusing, and most often, the diagnosis rests over the intraoperative findings and histopathological examination. The cyst's complete surgical resection remains the treatment of choice in patients with bulky, rapidly growing lesions or symptoms. Herein, we report a large retroperitoneal cystic lymphangioma that mimicked the mesenteric cyst clinically.