Using a gait mat, we characterized the functional results for thirty-five patients before and after a total knee replacement for the treatment of degenerative arthritis. Preoperatively, we studied three distinct populations of patients. Group I consisted of sixteen patients who were scheduled to have a unilateral total knee replacement and who had no signs or symptoms of arthritis in the contralateral knee. Group II consisted of twelve patients who were scheduled to have a unilateral total knee replacement but who had asymptomatic degenerative arthritis in the contralateral knee. Group III consisted of seven patients who had bilateral arthritis that was to be managed by total knee replacement. The gait mat allowed us to measure stance time, step length, double-support time, swing time, swing-to-stance ratio, and velocity. A knee-rating scale was used to measure pain. The data were compared with those obtained from an age-matched control group of ninety-one subjects. Postoperatively, the gait evaluation revealed marked improvement in all of the patients. However, the patients in Group II did not improve as much as those in Groups I and III did. We concluded that even asymptomatic arthritis can impair gait, that bilateral total knee replacement can yield excellent results, and that patients tend to use the lower limbs in as symmetrical a way as possible. Gait analysis can be an important source of objective information, and it is easily performed by using a gait mat.