Cystic lymphangiomas are benign tumors of the lymphatic vessels. It is characterized by its clinical polymorphism. Its retroperitoneal localization is rare. Its diagnosis relies mainly on imaging but needs histological confirmation. Its treatment is surgical. It can have an adverse evolution, especially when its volume causes compressive complications. We report the case of a 65-year-old male patient who presented abdominal distension and pain, whose abdominal scan showed a voluminous retroperitoneal mass. The interest of our case resides in the impressive volume of the tumor, its expressive scanographic semiology and its favorable evolution.