The objectives of this study were to examine the effects of the processing conditions, sterilization, and thermal treatment on the morphological and mechanical properties of ultra-high-molecular-weight polyethylene (UHMWPE) in medical applications by means of thermal analysis, Fourier transform infrared spectroscopy, and nanoindentation. It is well known that manufacturing, irradiation, and thermal treatments significantly alter the microstructure of materials, which results in changes in their mechanical properties. UHMWPE was found to be barely sensitive to processing conditions but strongly influenced by sterilization treatments. Great emphasis was given to the characterization of the so-called first generation of highly crosslinked UHMWPE because the thermal history of this material differed from that of c-irradiated materials. The physical and mechanical properties of UHMWPE were influenced as a result of c and electron-beam irradiation and the remelting procedure. Lower crystallinity, different lamellar thickness distributions, and lower hardness and modulus values were estimated. (c) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 120: 1875-1884, 2011