popliteal fossa. She received intra-articular injection into left knee joint through popliteal fossa for the gonarthrosis approximately 30 years ago. Arteriovenous fistula was diagnosed by duplex scan, and it was proved that the pulsatile mass was a venous aneurysm. Enhanced computed tomography and angiography showed an arteriovenous fistula arising from the left sural artery, but did not reveal the drainage vein. The surgical resection with posterior approach was chosen. An arteriovenous fistula between sural artery and vein, and a large venous aneurysm arising from sural vein at the level of the arteriovenous communication were proved during surgery. The sural venous aneurysm was resected and directly repaired. The sural artery including a fistula was dissected and its orifice was closed by patch angioplasty.