The 16-station RandomPOD pin-on-disk device with non-cyclic biaxial motion and load was used to study the effect of contact area on the wear of ultrahigh molecular weight polyethylene as used in total hip prostheses. The counterface was polished CoCr and the lubricant was diluted serum. The wear factor increased strongly and linearly with increasing contact area, which was in agreement with clinical findings for total hip prostheses. The coefficient of friction also increased strongly with increasing contact area. With small contact area the lumpy topography of the worn surface differed from the burnished appearance typical of retrieved acetabular cups. The nominal contact pressure should be kept below 2 MPa in pin-on-disk tests intended to simulate clinical wear mechanisms.