Twenty-four patients who had osseous lesions with histological features of both Ewing's sarcoma and osteosarcoma were studied. Because of their appearance, these lesions have been labeled small-cell osteosarcomas. They appear to represent a definite histological entity and the prognosis may be worse for these lesions than for conventional osteosarcomas. It is most important not to misdiagnose this tumor as Ewing's sarcoma because it appears not to be radiosensitive. Radical surgery and modern adjuvant chemotherapy seem to offer the best chance of cure.