Almost a quarter of a century has passed since mesenchymal chondrosarcoma, a rare, insufficiently studied and still poorly understood cartilage neoplasm has been described. Based on 35 cases diagnosed and treated at this Cancer Center, this study found 20 males and 15 females with an average age of 26 years (range, 6-70 years). All but five of the tumors arose in the skeleton in the femur, humerus, and ilium in five cases each, while the os calcis (a rare site for any other osseous tumor) gave rise to this tumor in four instances. Pain was the cardinal symptom in 27 patients. The lesional size varied from 4 to 18 cm (average, 9.5 cm). Histologic examination revealed nine of the tumors to be of the small cell undifferentiated types while the others were of the "hemangiopericytomatoid" variant. According to this subclassification, patients with the small cell type of lesions responded to combination chemotherapy and irradiation, as usually do other small cell sarcomas. The addition of surgical resection may be of value especially in the patients with the hemangiopericytomatoid variant. Preliminary results in the treatment of five such patients with evaluable disease suggest that this combined treatment approach is encouraging. Follow-up analysis of all patients revealed a 37.9 months median survival, and 28% to be alive at ten years.