127 patients with displaced fractures of the acetabulum were included in this study to examine the effectiveness of indometacin in reducing the incidence of heterotopic ossification (HO). Patients were randomized to receive indometacin sustained released (75 mg) or placebo daily for 6 weeks. After 3 months, there was no significant difference between the two groups for the incidence of HO and rate of complication. Patient compliance was significantly lower in the indometacin group than in the placebo group due to side effects. From the results, indometacin does not appear to be an effective method for the reduction of HO incidence 3 months after surgery in patients with displaced fractures of the acetabulum.