Fourteen knees in 11 individuals were studied before knee arthroplasty and at three and six months following surgery. Eleven of these knees were further evaluated at 12 months following surgery. At each evaluation, kinematic, electromyographic, and force plate data were gathered during level walking. Maximum knee extension and flexion torques were also determined. The greatest improvement in gait was noted in the first three postoperative months when velocity increased 13% and stride length increased 14%. After six months gait changes were negligible. Maximum knee torques in the osteoarthritic population were decreased at three months, then returned to preoperative levels at six months. In the rheumatoid population, maximum knee torques steadily increased up to six months following surgery. Gait abnormalities that persist at six months and beyond following knee arthroplasty appear to be most related to the presence of arthritis in joints other than in the operated knee(s).