The effect of post-irradiation shelf-aging time on the wear of UHMWPE was investigated, and wear results were correlated with the time-dependent microstructural changes of polyethylene after gamma irradiation sterilization. The levels of oxidation and crosslinking in the shelf-aged acetabular liners were examined by FTIR and hot xylene extraction, respectively, and uni-directional repeat pass sliding wear tests were conducted by using a pin-on-disc wear tester. Gamma irradiation sterilization in the air environment caused an increase of oxidation, crosslinking, and wear resistance. With aging, however, oxidation progressed and decreased the level of crosslinking. This resulted in a decrease of wear resistance of UHMWPE that was accompanied with white bands and brittle cracking.