The circulatory pattern of a skin flap was studied by microsurgical dissection, dye injection and angiography in 50 lower legs of fresh cadavers. The conclusions are as following: (1) The lateral sural cutaneors artery descends constantly and superficially accompanied by concomitant nerves. The upper post-lateral area of the lower leg in the best donor site of the flap. (2) The lateral sural cutaneous artery and the peroneal perforating artery form a anastomotic arcus around the lateral malleolus in 88.6% of the lower legs. The mean diameter of the anastomotic arcus is 0.63 +/- 0.19 mm. (3) The peroneal perforating vessel is 3.5 +/- 1.4 cm in length. Based on it the pedicle of the flap can be prolonged 6-8 cm on the main vessel of the lateral sural cutaneous artery. (4) Creation of the flap has no influence to the blood supply and function of the lower leg. (5) By anterograde transfer, the lateral sural island flap could be used to repair the defects around the knee and upper tibia. However, retrograde transfer of the flap has a higher clinical values in repiring the defects on the lower one third of lower leg and medial malleolus.