In designing femoral components which restore native (i.e. healthy) knee kinematics, the flexion-extension (F-E) axis should match the native knee. Because the F-E axis is governed by the curvature of articular surfaces of the femoral condyles in the sagittal plane, the primary objective was to determine variations in radii of curvature. Eleven high accuracy 3D femur models were generated from high-resolution CT scans. The sagittal profile of each condyle was created. The radii of curvature at 15 deg increments of arc length were determined based on best-fit segment circles. Results were standardized to the radius of the best-fit overall circle fit to 15 - 105 deg. Medial and lateral femoral condyles exhibited multi-radius of curvature sagittal profiles where the radius decreased at 30 deg flexion by 10 mm and at 15 deg flexion by 8 mm, respectively. On either side of the decrease, radii of best-fit segment circles were relatively constant. Beyond the transition angles, anterior-posterior (A-P) positions of centers of curvature varied 4.8 mm and 2.3 mm for the medial and lateral condyles, respectively. A two-radius of curvature profile approximates the radii of curvature of both native femoral condyles, but the transition angles differ with the transition angle of the medial femoral condyle occurring about 15 deg later in flexion. Owing to variation in A-P positions of centers of curvature, the F-E axis is not strictly fixed in the femur.