Fifty-nine patients with osteogenic sarcomas arising in bones following exposure to x rays and 20 patients with postradiation malignant fibrous histiocytomas of bones arising as a direct consequence of irradiation were studied. These represent 5.5% of all osteogenic sarcomas and 4.9% of all malignant fibrous histiocytomas of bones. The sarcomas may affect any skeletal site, but most commonly they arose in bones of the pelvic and shoulder girdles or the distal end of the femur. Grounds for irradiation were either nonosseous conditions or preexistent skeletal lesions. Reasons for incidental osseous irradiation included Hodgkin's disease, carcinoma of cervix, breast or lung; bilateral retinoblastoma and others, and giant cell tumor predominated among the irradiated skeletal lesions. The mean and the median radiation doses were 6,040 cGy (rad) and 5,700 cGy (rad), respectively. The period of latency between irradiation and the appearance of the bone sarcoma ranged from 3.5 to 47 y with a mean of 16.5 and median of 14.5, respectively. The cumulative disease-free survival rate for malignant fibrous histiocytoma patients at 3 y was 58%. The cumulative disease-free survival rate at 5 y for patients with osteogenic sarcoma was 17%, with a median survival estimate of 1 y. Although all patients with malignant fibrous histiocytoma who received their radiation therapy for a preexistent bone lesion survived, only 27% of the patients whose bone was normal at the time of irradiation are alive and well at the 3-y mark.