This PhD thesis studies the performance of metal-on-metal bearings, which are used in hip arthroplasty. Three aspects in particular were studied, namely the clinical results, the release of cobalt and chromium wear debris from the bearings, and the effects of this debris on a cell's DNA. The clinical results showed that large diameter metal-on-metal bearing hip resurfacing (BHR) restored hip function to an excellent level and had an extremely low failure rate up to eight years after the operation. This makes a metal-on-metal bearing an attractive option for hip replacementin high-demand patients.