185 patients undergoing primary total hip arthroplasty (THA) were included in this randomized controlled trial. Patients were randomized to receive either a large femoral head metal-on-metal THA or a conventional prosthesis. The purpose of the study was to compare clinical outcomes, dislocation and metal ion release at 2 years postoperatively. Enrollment in this study did not meet the pre-planned sample size of 330 patients. The results from the 185 included patients displayed comparable clinical outcomes at 2 years between groups and lower cobalt ion concentrations at 2 years in the large femoral head THA group. No signs of osteolysis and loosening were observed and 1 dislocation in the conventional THA group was observed. The results from this trial should be interpreted with caution due to the inability to meet the pre-planned sample size calculation.