Ectopic bone formation or heterotopic ossification (HO) is frequently seen on rehabilitation units after total hip arthroplasties, burns, and neurological injuries. Currently the major role for treatment is in prophylaxis and the major methods include anti-inflammatory medications, irradiation, and diphosphanate administration. These prophylactic measures are generally considered to be ineffective for the treatment of ectopic bone once it has already formed. We describe two cases of HO for which a radiation therapy protocol was used to treat established, ectopic bone after it had become problematic. Both patients were found to have increased range of motion and decreased complaints of pain after treatment, though no gross plain film x-ray changes were noted. We conclude that radiation therapy may be useful not only for prophylaxis of heterotopic ossification but for ectopic bone after it has been formed, especially when pain and progressively decreased range of motion are problematic.