The Oxford Meniscal Knee is an unconstrained surface arthroplasty that has given good clinical results. The biomechanics of knee function during walking in patients with this arthroplasty were examined using a three-dimensional television/force platform/computer system. Two groups of patients were studied: a retrospective group of 13 patients with single joint disease and a prospective group of 13 knee arthroplasties in 10 patients with mixed joint pathology. General gait parameters (cadence, velocity, and stride length) were near normal in the retrospective group and showed a useful improvement in the prospective group. In the sagittal plane the knee showed some limitation of extension and a tendency toward an abnormal flexion-extension moment pattern. In the coronal plane, the knee arthroplasty generally corrected errors of alignment, but about one-third of the patients had adduction/abduction moments outside the normal range. The clinical results of the arthroplasty are thus better than the biomechanical results, an observation common to all of the knee arthroplasties that have been studied using comparable methods.