Atomic force microscopy is proposed and explored as a technique for the characterisation of ultra-high molecular weight polyethylene (UHMWPE) wear particles from knee prostheses. This new approach may be an alternative to other techniques such as filtration and scanning electron microscopy. Atomic force microscopy can measure the size and geometry of polyethylene wear particles extracted from the joint lubricant with a precision on the nanometre-scale. This can further the understanding of wear processes at this length-scale. However, information about the absolute and the fractionated abundances of the particles in the lubricant is lost, since the particles precipitate non-uniformly on substrates suitable for atomic force microscopy. It is demonstrated that conventional filtration of polyethylene particles can cause similar non-uniform precipitation on a filter medium. This result gives support to the view that uniformity across a substrate or filter medium needs to be established in detail and quantitatively using an appropriate experimental protocol so that abundance distributions may be obtained reliably.