Retroperitoneal schwannoma is a rare tumor originating in the neural sheath. We report the case of a 48 year-old women. She had a ten year history of lumbal pain. The abdominal sonography had revealed a left retroperitoneal tumor that compresses the left renal cavities. The abdominal CT scan visualized a 56 mm, homogenous, well demarcated, retroperitoneal mass with a low attenuation. This mass with multiple enhanced septa is separated from the left adrenal gland. The diagnosis of a cystic lymphangioma is made. We perform surgical exeresis of the tumor by a left lumbal laparotomy. The pathology examination concludes in an altered schwannoma with Antoni B patterns. Retroperitoneal schwannoma is a primary neural benign tumor with a good prognosis. The management is surgical.