Heterotopic ossification after hip arthroplasty can be prevented by ibuprofen given 3 months postoperatively. To evaluate the effectiveness of 10 days of ibuprofen treatment we performed a randomized, double-blind, prospective study on 57 patients with primary arthrosis, undergoing total hip arthroplasty. 47 patients completed the study and no effect on the incidence of ossification could be detected.