A case of extraskeletal Ewing's sarcoma arising in right lumbar region with involvement of epidural space is described in a 16 years old girl. The diagnosis of Ewing's sarcoma was done from cytochemical and electron microscopic studies which showed intra-cellular glycogen granules whereas cytologic and immunological analysis eliminated lymphoid malignancies. This case emphasized the interest of these techniques, adjunctive to routine light microscopic examination for the pursuit of a specific diagnosis in the small round cell neoplasm.