An unusual presentation of secondary malignant fibrous histiocytoma of the femur in a patient with diaphyseal medullary stenosis is described. The patient, a 42-year-old man, presented with a painful lump in the right knee. A radiograph of the right femur showed lytic destruction. Characteristic features of longitudinal linear striations in the metaphysis and medullary stenosis in the diaphysis were observed in radiographs of the long tubular bones. A radiograph of the pelvis showed bilateral acetabular bone scleroses. After chemotherapy, surgical resection was done. On light microscopic examination, the tumor had features characteristic of malignant fibrous histiocytoma. Specimens from the diaphyseal medullary stenosis from the femur and tibia showed typical features of bone infarction. Radiographs of other members of the patient's family showed similar features of linear striation, cortical bone thickening, and acetabular sclerosis, including wavy, open growth plate of the iliac crest. The patient's aunt had died of a bone sarcoma in the shoulder region. It is important to recognize this extremely rare clinicopathologic type of diaphyseal medullary stenosis that frequently is associated with secondary high-grade sarcomas.