Traumatic iliac arteriovenous fistulas (AVFs) are extremely rare, with only two cases reported in literature involving the internal iliac artery and the external iliac vein. We report the case of a 23-year-old man who sustained a gunshot injury to the left lower quadrant of his abdomen and subsequently developed unilateral leg edema of "elephantiasic proportions." Intra-arterial digital subtraction angiography six years later was essential for diagnosis and comprehension of the pathomechanism. The angiographic examination showed an internal iliac false aneurysm, as well as a high-flow arteriovenous communication between the left internal iliac artery and external iliac vein complicated by thrombotic occlusion of the left common iliac vein. The initial vascular injury and the surgical management of simple ligation were thought to be responsible for the iliac AVF and the subsequent thrombosis of the common iliac vein. On the one hand, the thrombotic occlusion of proximal vein led to a sharp increase of mean pressure in the proximal and distal arteries and in the distal vein, resulting in chronic venous insufficiency with incompetent varicose veins. On the other hand, the restriction of venous outflow produced extreme peripheral edema and large superficial veins serving as collaterals to bypass the fistula. Vascular surgery could repair the lesion by closing and bypassing the AVF.