Case: Heterotopic ossification (HO) is a pathological formation of bone in nonosseous tissue and is a common complication of orthopaedic procedures. Radiotherapy is often used to prevent HO despite the small risk of secondary malignancy. Here, we report a case of a patient who developed a periprosthetic, radiation-induced sarcoma after delivery ofasinglefractionof7GyforHOprophylaxis.This sarcoma was found to lie entirely with in the treatment field and occurred within 5 years of radiation. Conclusion: Appropriate counseling regarding radiation-induced sarcoma formation should be provided to patients considering radiotherapy for this HO prophylaxis. [ABSTRACT FROM AUTHOR]