One of our major goals in total knee arthroplasty seems to be the perfectly aligned knee, which means a mechanical axis of 180° degrees between the femur and tibia. Do we really have to aim for a perfectly straight leg? It might be true from the biomechanical point of view in order to achive an almost equal loading in the medial and lateral compartment of the knee. What about the function of the knee? Recent studies have shown that the natural knee is not always neutrally aligned. There is a certain percentage in our population with a constitutional varus aligned knee. Do we need to consider the natural leg alignment of the patient when TKA rugery is planed? What about severe varus and valgus malalignment due to osteoarthritis or maldeformity, which patients may present for many years before they come for surgery? Do we have to pay more attention to the anatomy of the knee and the entire lower limb? There are many open questions and this symposium will help to bring more light into the dark box of leg alignment.