In a 42-years-old woman, an abdominal sonography was done, and a 10 x 9-cm solid cystic tumor on the left kidney appeared. Abdominal CT and arteriography showed a retroperitoneal heterogeneous mass surrounding and obstructing the ureteropelvic left junction. Tumor was removed under open surgery and the pathological study showed a benign schwannoma. We present this case because of its rarity 1%-10% of all primary retroperitoneal tumors.