Malignant neuroepithelioma is a rare neoplasm arising within the peripheral nervous system and usually occurs in the lower extremities. It may involve patients in any age group and have no gender predisposition. In adolescents and adults the tumor must be distinguished from other malignant round-cell tumors. The poor prognosis and the need for aggressive, combined surgical and chemotherapeutic modalities in treating this tumor necessitate a prompt and accurate diagnosis. Authors have experienced a case of malignant neuroepithelioma developed in left sciatic nerve. The diagnosis was confirmed by CT scan, M.R.I., light and electron microscopic findings.