Background <p>The preferred technique for femoral implant sizing in primary total knee arthroplasty (TKA) is debatable. Sizing is based on the anterior femoral cortex or posterior condylar reference. Using a single knee system, this study compared anterior referencing (AR) versus posterior referencing (PR) in patients undergoing simultaneous bilateral TKA, where one reference technique was randomized to each knee.</p> Methods <p>This prospective study compared the two sizing references using one posterior stabilized knee system. The study included 81 subjects with osteoarthritis and similar varus deformity in both knees. All subjects underwent identical surgical procedures, aside from the selected femoral sizing reference. Subjects were followed for at least 2&#xa0;years.</p> Results <p>The two sizing techniques did not significantly differ in all measured radiographic, operative, and clinical parameters. The mean posterior condylar offset ratios were similar. Two-year mean knee flexion and Revised Oxford Knee Scores showed no difference. Eighty-four percent of patients stated no preference for either technique.</p> Conclusion <p>Knees sized with anterior referencing had similar functional outcomes to those sized with posterior referencing. Using a current knee system with multiple sizing options, there is no discernable difference in all measured study parameters. Either reference is acceptable.</p> <p><i>Level of Evidence</i> 2 (Randomized cohort study).</p>