Aims: To evaluate clinical and radiographicl results of hydroxyapatite versus porous coated stems in total hip arthroplasty. Methods: A consecutive randomized series of 447 cementless Titanium prostheses were prospectically studied. The stems (Synergy-Smith& Nephew) were different for the proximal 1/3 hydroxyapatite (HA=268) or titanium porous coating (PC=179) Same cup and ball head were used. Clinical (HHS/Womac) and radiological assessments (Enghñs criteria) were obtained before and after surgery (mean F-U=27,05 months). Results: The clinical outcomes showed a signiþcant improvement in both groups. Bone ingrowth was present in 100% (HA) and 96% (PC) and stable þbrous ingrowth in 4% (PC). Cortical hypertrophy and heterotopic ossiþcation (Brooker 1) were prevalent in HA without limitation of ROM or pain. Stress shielding was equivalent. Nor osteolysis neither subsidence were identiþed. Fractures occurred in 8 cases (HA=6/PC=2) and dislocation in 3 cases. Conclusions: In this study the two types of stems showed good comparable clinical results. The complication were not related to the coating. HA coated prosthesis showed faster osseointegration, and enhanced bone ingrowth. The earlier bone-stable integration obtained in the HA group may be predictive of a lesser degree of osteolysis in the future