We report a case of a malignant peripheral nerve sheath tumor arising in the distal femur of a 28-year-old man who had no stigmata of von Recklinghausen's disease. Roentgenograms and computed tomographic scans of the distal femur showed a single lytic intraosseous lesion with minimal soft tissue extension. Light microscopy demonstrated a tumor composed of spindle cells with myxoid areas. There was some nuclear pleomorphism and mitotic activity. The tumor cells were immunoreactive for S100 protein and neuron-specific enolase. Ultrastructurally, there were cells with long processes, which were focally invested by basal lamina. Some cells had numerous micropinocytotic vesicles. The tumor recurred in the femur 15 months following the initial curettage. Computed tomographic scan of the lungs at that time showed a nodule, which has since enlarged. Primary osseous malignant peripheral nerve sheath tumors are uncommon. A literature review revealed only 18 previous cases, the majority of which occurred in the mandible or maxilla. This is a rare case of intraosseous malignant peripheral nerve sheath tumor of a long bone, with both immunohistochemical and ultrastructural confirmation of nerve sheath differentiation.