Osteogenic sarcoma is a convenient and generically correct designation for all skeletal conective-tissue neoplasms of mesenchymal origin including: osteosarcoma, chondrosarcoma, fibrosarcoma, parosteal osteogenic sarcoma, and osteogenic sarcomata arising in Paget's disease, irradiated bone, Osteochondroma, fibrous dysplasia, or other bone disease. This report is summary of the clinical, histopathological, and roentgenographic findings, and of the treatment and end-results of treatment in 552 cases of osteogenic sarcoma. Factors which have no influence on prognosis are age, sex, bone of origin, trauma, and the occurrence of fracture. Factors which do influence prognosis include: histological type of sarcoma, tumor size, preoperative and postoperative serum alkaline Phosphatase elevations, lymph-node involvement, and treatment. Absolute five-year survival figures varied from 0.0 per cent for osteogenic sarcoma arising in Paget's disease to 82 per cent for parosteal osteogenic sarcoma; the figures for the other types were as follows: osteosarcoma, 13.2 per cent; chondrosarcoma, 28.1 per cent; fibrosarcoma, 31.7 per cent; and secondary chondrosarcoma, 67 per cent. Only in chondrosarcoma did grading correlate with prognosis; the patients with low-grade and medium-grade chondrosarcoma having considerably better survival rates than those with high-grade tumors. The incidence of late failures (patients dying of sarcoma more than five years after diagnosis) showed an inverse relationship to five-year survival. Prognosis varied directly with tumnor size, and no patient with an osteosarcoma or fibrosarcoma greater than 15.0 centimeters in greatest dimension was cured. When examination of the surgical specimen revealed lymph-node metastases, the outcome was always fatal. Radical ablative surgery is the only curative therapy for osteogenic sarcoma. Irradiation as the sole therapy did not cure a single patient. Preoperative irradiation followed by radical ablative surgical therapy was attended by a worse prognosis than surgery alone. Two patients with unilateral lung metastasis were cured by lobectomy. Adjuvant chemotherapy by perfusion administered prior to radical ablative surgery might be considered for future investigative protocols.