Objective gait analysis was used to develop a functional performance index for patients with hip disease. Bilateral hip joint motion was measured using 3-D electrogoniometers. A force platform, instrumented walkway and foot switches were utilized to determine key temporodistance factors and ground reaction forces. Clinical parameters were also collected in order to calculate the Harris hip score. Fifty preoperative total hip replacement patients with hip disease and thirty-one sex and age-matched normals were studied.