The aim of this study was to determine if radiation prevents heterotopic ossification (HO) in HO-forming patients after total hip arthroplasty (THA) or HO excision alone. Patients with HO in the ipsilateral hip (63 treated with THA revision and 25 treated with HO excision alone) and HO in the contralateral hip (36 treated with primary THA) were termed HO-forming patients. They underwent radiation to prevent HO. After excluding patients with inadequate follow-up, 84 patients were studied to determine if radiation prevents significant HO (Brooker Grade 3-4). For patients with ipsilateral hip HO, 12.3% developed significant HO. In patients with contralateral hip HO, 10.5% developed significant HO after THA. Sixty percent who received 6 Gy in 3 fractions after excision of ipsilateral HO developed significant HO, which was higher than for all dose-fractionation schemes combined (P = .01). In contrast, patients who received 7 Gy in 1 fraction developed significant HO 13.8% of the time, which was equivalent to all dose-fractionation schemes combined (P = not significant). Radiation prevents HO in HO-forming patients.