Retrievals obtained after revision surgery, provide valuable information on the rate of wear and the causes of wear that take place in vivo. The aim of this study was to perform a root cause failure analysis to determine the principle reason for mechanical failure on failed acetabular cups, retrieved during revision surgery, by making use of sound engineering failure analysis techniques. The bearing couples varied between steel on UHMWPE and ceramic on UHMWPE. The information gained during this analysis brought to the fore that the principle mode of mechanical failure for acetabular cups is overheating of the UHMWPE. The resulting overheating is mainly due to a lack of good and/or sufficient lubrication.