Two cases of osteogenic sarcoma arising in irradiated bone are reported. They developed in patients treated at the University of California for carcinoma of the breast and of the cervix. Both occurred in previously normal bone. The latent period was eleven years in one and five years in the other. To evaluate the incidence of this complication, the number of malignant tumors irradiated at this hospital and the number of five-year survivors were determined. Of almost 6,000 patients treated, sarcomas developed in only 2, an incidence of 0.03 per cent or 0.1 per cent of the 2,300 five-year survivors. Although radiation-induction of bone sarcoma apparently does occur in normal bone, it is a rare complication of radiation therapy for malignant disease.