Osteogenic sarcoma is the most common type of primary malignant tumor of bone. In the American Registry of Bone Tumors it is represented by the largest number of reported cases, namely, 1,071 out of a total of 2,232 cases. Mercer1 estimated its incidence as 1 in 75,000 of the general population. At the University Hospital during the period from 1925 to 1938, inclusive, this diagnosis has been established in 80 of 305,760 consecutive hospital registrations, an incidence of 1 to approximately 3,800 registrations. It is believed that osteogenic sarcoma was seen in more cases during this period, but in the additional cases the criteria for diagnosis were not sufficiently well established to warrant inclusion of these cases in this series. GENERAL CONSIDERATIONS Osteogenic sarcoma is primarily a disease of the young. In 40 of our cases, or 50 per cent, it occurred in the second decade of life. The