A consecutive series of 145 central-type osteogenic sarcomas in the long bones of patients under the age of twenty-one years was studied by analysis of the interval from surgery to onset of pulmonary metastasis and the interval from the onset of pulmonary metastasis to death. The effects of the time of surgery, age, sex, race, preoperative duration of symptoms, location of tumor, and preoperative radiation on the course of the disease were analyzed. One hundred and twenty-one patients had pulmonary metastasis prior to the end of the study and died of their disease. Twenty-four patients were free of metastasis at the end of the study. The five-year survival rate was 17.4 per cent. Age and location of the tumor were found to affect the time of onset of pulmonary metastasis but not the five-year survival figure. The first two years after definitive surgery were shown to be the critical period for studying the course of the disease. The data analyzed in this study may offer a valuable control series against which future methods of treatment can be evaluated.