The efficacy of a 10-day course of indomethacin in preventing heterotopic ossification after total hip arthroplasty was studied in a consecutive series of male patients who were at increased risk for bone formation. Between September 1991 and June 1994, all male patients (123 hips in 109 patients) who underwent total hip, revision, or surface arthroplasty were placed on a 10-day course of indomethacin. Of these, 106 patients (119 hips) successfully completed the 10-day course. There was no significant formation of heterotopic ossification (Brooker grade III or IV). From a group of 45 known heterotopic bone formers following previous total hip arthroplasty, only 2 developed new heterotopic ossification. Overall there were 9 (7.6%) new cases of heterotopic ossification: 7 Brooker grade I (5 primary and 2 revision cases) and 2 Brooker grade II (both primary cases). A 10-day course of indomethacin prevents the more significant grades of heterotopic ossification and is effective at reducing the incidence of heterotopic ossification following total hip arthroplasty. Further, this regimen appears safe and cost effective.