An historical prospective study was performed to compare two surgical management alternatives in the treatment of patients with knee arthritis. There were 120 unicompartmental and 81 tricompartmental knee arthroplasties in 98 and 66 patients, respectively. All living patients were available for follow-up observation, and survivorship data on all arthroplasties were obtained. The average follow-up interval was 78 months (range, eight-162 months) in the unicompartmental series and 68 months (range, two- 186 months) in the tricompartmental group. Patients receiving the unicompartmental arthroplasty were treated with nonmetal-backed polyethylene tibial components. Prosthetic survivorship was 92% at ten years in the unicompartmental patient group. There were no statistically significant differences in aseptic loosening between these two patient groups. In appropriately selected patients unicompartmental arthroplasty was associated with better range of motion and ambulatory function than patients being treated with tricompartmental knee replacement.