41 patients were randomized to determine the difference in metal ion release between metal on metal and metal on polythethylene articulation in total hip arthroplasty. Patients received either a metal or polyethlyene acetabular component, and were followed up for a minimum of 10 years for clinical, radiographic, and metal ion concentration outcomes. Results at 10 year follow-up indicated that metal on metal articulation led to significantly greater levels of erythrocyte cobalt, urine cobalt, and urine chromium compared to metal on polyethylene bearings. However, the increases were not associated with any component failure, revision surgery, or patients diagnosed with metal hypersensitivity.