The perforating veins connect the deep and the superficial vein system. If on the one hand the blood flows from the superficial veins into the deep veins, the normal transport function is sustained. On the other hand, if it flows from the deep veins into the superficial vein system, this might be a sign for valve weakness, which are frequently accompanied with the formation of varicose veins. Perforating veins are frequently successfully treated by the means of sclerotherapy.