A case of retroperitoneal benign schwannoma is presented; in addition, 133 cases of retroperitoneal schwannoma reported in Japanese literature are studied. In our series 66 per cent of the cases were found to be cystic. Therefore, the cystic change may be one of the preoperative features of schwannomas, because other types of retroperitoneal tumor do not frequently form cysts. Furthermore, the necessity of postoperative electron microscopy for accurate histologic diagnosis is discussed.