The purpose of this study was to examine the effects of ceramic femoral head material, size, and implantation periods on the wear of annealed, cross-linked ultra-high molecular weight polyethylene (UHMWPE) (XLPE) in total hip arthroplasty compared to non-cross-linked conventional UHMWPE (CPE). XLPE was fabricated by cross-linking with 60 kGy irradiation and annealing. Femoral heads made from zirconia and alumina ceramics and cobalt-chrome (CoCr) of 22 or 26 mm diameter were used. In this retrospective cohort study, the femoral head penetration into the cup was measured digitally on radiographs of 367 hips with XLPE and 64 hips with CPE. The average follow-up periods were 6.3 and 11.9 years, respectively. Both XLPE creep and wear rates were significantly lower than those of CPE (0.19 mm vs. 0.44 mm, 0.0001 mm/year vs. 0.09 mm/year, respectively). Zirconia displayed increased wear rates compared to alumina in CPE; however, there was no difference among head materials in XLPE (0.0008, 0.00007, and À0.009 mm/year for zirconia, alumina, and CoCr, respectively). Neither head size or implantation period impacted XLPE wear. In contrast to CPE, XLPE displayed low wear rates surpassing the effects of varying femoral head material, size, implantation period, and patient demographics. Further follow-up is required to determine the long-term clinical performance of the annealed XLPE. Keywords: polyethylene; wear; total hip arthroplasty; cross-linked; annealing Osteolysis is related to particulate ultra-high molecular weight polyethylene (UHMWPE) wear debris and is considered an important cause of aseptic loosening and late implant failure in total hip arthroplasty (THA). 1-3 Thus, UHMWPE wear is one of the major determinants influencing THA survivorship. Highly cross-linked UHMWPE (XLPE) is an alternative bearing surface developed to improve wear resistance and decrease osteolysis. XLPE has been studied extensively in vitro and has substantially decreased wear rates compared to non-cross-linked conventional UHMWPE (CPE) in hip simulator studies. 4,5 Preliminary clinical studies of XLPE in patients undergoing THA have confirmed these promising findings with a 30-80% reduction in wear compared to CPE at 3-5 years. 6,7 XLPE is fabricated using irradiation at 50-100 kGy for cross-linking and thermal treatment after irradiation to reduce free radicals and increase durability and cross-link density. Methods to prepare XLPE include radiation (gamma ray or electron beam), thermal treatment (remelted or annealed), and sterilization. 8 These methods, which influence mechanical properties, crystallinity, and oxidation states, are not equivalent, and the resulting clinical performances differ.The type of material and the size of femoral head are additional factors that influence wear. 9-12 Cobaltchromium alloy (CoCr) replaced stainless steel and titanium alloy due to its high wear resistance. 13