Alumina hip replacement prostheses have been analyzed following in vitro simulated microseparation. The worn surfaces of the alumina acetabular cup and femoral head were investigated using scanning electron microscopy (SEM) and atomic force microscopy (AFM) which identified four different wear zones. Focused ion beam (FIB) cross-sectioning was used to section the worn surface and produce 3D reconstructions of the subsurface damage. This showed that the subsurface fracture was predominantly intergranular, with occasional intragranular fracture. Significantly, in all cases, fracture was restricted to the outer layer of grains. The wear mechanisms leading to the generation of the stripe wear region on the worn alumina hip prostheses are proposed and microseparation is believed to play a critical role. © 2011 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2012.