Sixty-six patients with well-documented osteogenic sarcomas arising in bones and soft tissues after exposure to x-rays, which represent approximately 5.5 percent of all osteogenic sarcomas registered since 1921 at this institution, were studied. These secondary sarcomas occurred in equal proportion in both sexes, with the sixth decade of life being the most common age. In 42 patients, the bone had been normal at the time of irradiation, whereas in 24, the radiation was directed against an osseous tumor or tumor-like lesion. The median latent period was 10.5 years in both groups, ranging from 3.5 to 33 years. The radiation varied from diagnostic quality to 1 MeV x-rays. The dose was variable, but none was less than 2000 rads. Postradiation osteogenic sarcomas most commonly arose in the bones of the pelvic and shoulder regions. Histologically, the sarcomas were mostly of the fibrous type (46%) and radiographically showed a destructive bone lesion with or without signs of radiation osteitis. The cumulative disease-free survival rate at 5 years was 17%, with a median survival estimate of 1 year.