Heterotopic ossification(HO) is a frequent complication of total hip arthroplasty(THA), If it is sevre enough, it can convert a successful result of the operation into a poor one. Among several strategies that researches in recent years have tested, radiation therapy have been accepted to have efficacy for prevention of heterotopic ossification by many authors. While postoperative irradiation has been shown to lower the incidence of HO effectively in high risk patients following THA, patients in multiple dose protocols continue to develop some heterotopic ossifiction despite therapy and have some problems. Ninteen patients received single dose exposure to 600 rad delivered within 48 hours of THA with shielding of prosthesis region. The patients were considered high risk group for developing HO because of hypertropic osteoarthritis, post-traumatic osteoarthritis or the presence of previous formed ectopic bone. The average follow up period was 10.2 months(range 6 months - 2 years). At follow up study, all hips except one were classified as class 1. All patients were asymptomatic at last follow up study and no component demonstrated subsidence or radiolucent line indicative of loosening. The authors concluded that 600 rad, single fraction radiation therapy is cost effective, convenient and safe for prevention of HO after THR.