Gait asymmetry is observed after total knee replacement, often leading to excessive forces at the contralateral limb. The number of total knee replacement procedures has increased substantially over the past 2 decades, particularly among younger patients. Relatively little is known regarding these younger patients (<65 y), specifically, with respect to gait asymmetry. The purpose of this study was to investigate if age affects gait asymmetry after unilateral total knee replacement. Three-dimensional analysis of 10 walking trials was collected from the following 4 groups: younger patient (age: 54.3 [7.9] y), younger control (age: 55.2 [4.0] y), older patient (age: 76.9 [4.7] y), and older control (age: 77.7 [4.1] y). The older patients, but not any of the other groups, demonstrated a significantly larger heel strike transient and peak knee adduction moment at the nonsurgical compared with the surgical limb. The observed gait pattern of the younger patients resembled that of the younger controls, rather than the older patients. The greater loading of the nonsurgical limb for the older patients could contribute to the initiation or further progression of osteoarthritic degeneration in the contralateral knee; these asymmetries were not observed for the younger patients.