98 patients with an acetabular fracture were included in a study to examine the effects of indomethacin on the prevention of heterotopic ossification (HO). Patients underwent open reduction and internal fixation through a Kocher-Langenbeck approach. They were then randomized to receive placebo for 6 weeks (group 1), 3 days of indomethacin followed by placebo for a total of 6 weeks (group 2), 1 week of indomethacin followed by 5 weeks of placebo (group 3), or 6 weeks of indomethacin (group 4). Over 1 year, the incidence of HO based on radiographic analysis was significantly higher in group 1 than in group 2 and 3. However, the groups did not differ significantly with respect to CT volumetric analyses, the occurrence of clinically significant HO, incidence of posterior wall nonunion, and range of motion. Pain scores were significantly higher in patients who had posterior wall non-union than those who did not. The results did not provide any evidence for the effectiveness of indomethacin, and the medication, therefore, cannot be recommended for the prevention of HO.