This paper reports the analysis of the articular surfaces of the femur and the tibia in normal knees. Six cadaveric joints were digitized with FARO Arm electrogoniometer and elaborated off-line fitting the profiles of multiplanar sections with least square curves. We found that: the femoral medial condyle can be represented by an ellipsoid with its main axis in the AP direction, semi-axes equal to 30 and 23 ±2 mm (roughly spherical posteriorly) and circular ML section (radius = 20 ±2 mm); the tibial medial plateau can be approximated by a semi-cylinder with its main axis in the AP direction and circular ML section (radius = 22 ±1.3 mm); the femoral lateral condyle can be represented by a ellipsoid with semi-axes equal to 26 and 20 ±4 mm and an elliptic ML section with a sloped major axis parallel to the tibial spine; the articulating tibial surface in the lateral compartment is approximately flat.