INTRODUCTION. Limb salvage surgery is a common treatment for patients who suffer from bone tumors. In the case of pelvic tumors this creates a challenge for the surgeon and the treatment remains controversial because the oncologic complications like local recurrence, dissemination and orthopaedic ones, like infection, haemorrhage, and mechanical problems of reconstructions Tumors affecting the acetabulum are a challenge for the surgeon because of the impact in the function of the extremity. There are many reconstruction techniques described in the literature like prosthesis, allograft systems, arthrodesis, etc…, but still there is not a gold standard due to the poor functional results at long term follow up, and the associated complications of all techniques. In this study we show the experience in our center on pelvic reconstructions after tumors affecting the acetabulum area (zone II). MATERIAL AND METHODS. We surgically treated 81 pelvic tumors from 1997 to 2009 following the Enneking and Dunham calssification attending to the localization of the tumor: Zone I 38 (iliac bone)Zone II 25 (acetabulum)Zone III 18 (pelvic branches)In zone II tumors we performed pelvic reconstruction in eight cases, with different type of prosthesis. In 5 cases we performed saddle prosthesis (group A) and in 3 cases we performed Coned-Stanmore Implants type prosthesis with sacro-iliac anchorage. The mean follow up of the serie was 3,5 years (1–6 years). In group A the mean follow up was 5 years and in group A and in group B the mean follow up was 1 year due to the recent implantation in our center of Coned type prosthesis for pelvic reconstruction. We evaluated our results with these two types of prosthesis. RESULTS. Oncologic: group A we had a local recurrence of 25% and 25% of the patients died. group B we had no cases of local or systemic recurrence and we didn't registered any death. Functional: In group A the patients showed local pain and difficulty to walk probably due to the change of the center of rotation of the hip and instability of the saddle prosthesis. In group B all patient's followed physical therapy programs without problems and were able to walk with crutches ten months after surgery. Complications:group A we had a 25% of perioperative infection and a 25% of dislocation of the prosthesis. In group B we did not have any of these complications. CONCLUSIONS. Saddle prosthesis mantain the length of the extremity and allow weight bearing but they do not give a good stability. Even if we only have one year follow up with this Coned prosthesis with sacro iliac anchorage we achieved much better functional results and a lower rate of complications