The anteroposterior (AP) and medial-lateral (ML) dimensions of 200 consecutive osteoarthritic knees (100 males and 100 females) undergoing unilateral primary total knee arthroplasty were compared. For all patients, the mean AP dimension was 57.3 mm (range: 49-66 mm) and the dimension was 10.5% taller in height in men than women. The mean ML dimension was 71.6 mm (range: 56-85 mm), and the dimension was 13.7% wider in men than women. The mean AP/ML ratio was 0.8 for all patients, 0.82 (range: 0.73-0.93) for females and 0.79 (range: 0.70-0.89) for males (P<.001). The data suggest that for any given AP femoral dimension, women tend to have a narrower ML dimension than men, independent of AP height, and an AP/ML ratio of 0.80 most closely approximates a standard-sized distal femur across gender. This report documents important gender differences that may serve as a reference for femoral implant designers and knee surgeons.