The primary venous drainage of the pelvis is provided by the internal iliac veins and their tributaries. The tributaries of the internal iliac vein are almost synonymous with the branches of the internal iliac artery. The internal iliac veins run medial to the internal iliac arteries, and the veins of the pelvis also follow a course close to the arteries. The internal and external iliac veins join to form the common iliac veins, which, in turn, join to form the inferior vena cava at about the level of L5.