Heterotopic ossification (HO) is detained as the development of abnormal ossification in soft tissues. HO is a common disease after total hip replacement. Many therapeutic modalities have been proposed to prevent HO. The most commonly used modalities are non-steroidal anti-inflammatory drugs (NSAID) or ionizing radiation administered just before or immediately after total hip replacement. As far as external radiation therapy is concerned, there are several published randomized studies aimed at investigating its efficacy and timing related to surgery, and at comparing ionizing irradiation to NSAID. In this article we review the published data in order to define guidelines which could be used in daily practice for the choice of prophylactic treatment against HO.