We present a study comparing etidronate or indomethacin for the prevention of heterotopic ossification after total hip arthroplasty in patients with hypertrophic osteoarthritis. 52 patients were divided in two groups. Group A (26 patients) received etidronate (20 mg/kg/day for 12 weeks) and Group B (26 patients) indomethacin 75mg/day for 2 weeks. Mean follow up was 36 months (range, 18 to 50 months). The incidence of side effects was 15.4% in group A and 30.8% in group B (p= 0.324). At 6 months there was no statistically significant difference in terms of clinical (p= 0.532) and radiographic evaluation between the two groups (p= 0.303). However, the cost of etidronate which may be as much as six times more expensive than that of indomethacin could not justify its routine prophylactic use.