From 1981 to 1986, 23 patients (24 hips) were treated with single-dose irradiation after hip surgery in an attempt to prevent heterotopic bone formation. All patients were at high risk for the development of heterotopic ossification because of the presence of heterotopic bone in either hip secondary to trauma or previous surgery, ankylosing spondylitis, or hypertrophic osteoarthritis. Thirteen patients (14 hips) underwent primary total-hip arthroplasty, and ten patients underwent revision total-hip arthroplasty or excision of heterotopic bone. The minimum follow-up period was 6 months. All patients were treated by means of a linear accelerator with a single dose of 700 cGy, calculated at midplane. Almost all treatments were given within 72 hours after surgery. Recurrent disease of Brooker grade II type developed in only one (4%) patient. This result is comparable with outcomes reported after fractionated courses of postoperative radiation therapy delivered over a period of 1 or 2 weeks. Postoperative hip irradiation with a single 700-cGy dose appears to be as effective as fractionated courses of radiation in the prevention of heterotopic bone formation in patients at high risk for the development of this complication.