Four hundred and thirty patients who had pathologically verified osteogenic sarcoma and who were treated at the Mayo Clinic from 1909 through December 1955, form the basis of this report. Patients with juxtacortical or parosteal sarcoma and osteogenic sarcoma of the jaw were not included in the series. Data on location of the tumor, age and sex of the patient, tumor type, grade of malignancy, and survival are given. Ninety-seven per cent of the patients were traced and adequate follow-up data were obtained. Osteogenic sarcoma is defined as a malignant lesion of bone, the proliferating neoplastic cells of which produce osteoid. It is the most commonly encountered malignant primary tumor of bone, exclusive of multiple myeloma. It may be classified microscopically as osteoblastic, chondroblastic, or fibroblastic. It must be especially differentiated from chondrosarcoma, fibrosarcoma, heterotopic ossification (myositis ossificans), fibrous dysplasia, non-osteogenic fibroma, and giant-cell tumor. Treatment in this series usually consisted in amputation. Local resection was performed in some cases and biopsy alone in some; radiation therapy was frequently used in conjunction with these surgical procedures. Of the entire group of patients with osteogenic sarcoma, 19.3 per cent survived five years and 15.3 per cent survived ten years from the date of definitive treatment. The corresponding rates for patients with lesions readily amenable to amputation (below the upper third of the femur) were 22.8 per cent and 17.6 per cent, respectively. The five-year survival rate for patients with lesions of the tibia was 34.6 per cent, while the rate for patients with lesions of the middle and lower thirds of the femur was only 17 per cent. Patients who had osteoblastic osteogenic sarcoma had the poorest five-year survival rate (15.6 per cent) when compared with those who had chondroblastic or fibroblastic sarcoma. There was a definite relationship between grade of tumor (Broders' method) and survival, the five-year survival rate being 25.4 per cent for patients with grade 1 and grade 2 tumors and I 7.6 per cent for those with grade 3 and grade 4 tumors. The five-year survival rate of nearly 20 per cent obtained for the emitire series of patients with osteogenic sarcoma seems to be extremely significant, especially when it is compared with other published data showing lower survival rates. Our figures have statistical importance because of the large number of patients traced. The treatment of osteogenic sarcoma that has been most successful in our hands is early surgical ablation. We see no theoretical or proved reason at present for any other form of therapy. unless amputation is not possible.