Four Level I randomized controlled trials (412 hips with a frequency weighted mean patient age of 57.8 years and a frequency weighted mean follow-up time of 5.7 years) were selected for a systematic review comparing metal-on-metal (MOM) with conventional metal-on-polyethylene primary total hip arthroplasty (THA) with respect to functional and radiographic outcomes. There was no significant difference between MOM and conventional THA with regard to functional outcomes as measured by Harris hip scores and radiographic outcomes as measured by radiolucent lines. Patients with MOM THA did, however, demonstrate a 3.37 times greater complication rate (7.26% vs 1.57%).