The internal iliac vein is a major blood vessel located in the pelvis. It collects deoxygenated blood from the pelvic organs, including the bladder, rectum, and reproductive organs. This vein runs alongside the internal iliac artery, and together they play a crucial role in the venous drainage of the pelvis. Once the internal iliac vein gathers blood, it merges with the external iliac vein to form the common iliac vein. This common iliac vein then drains into the inferior vena cava, which carries blood back to the heart. Proper functioning of the internal iliac vein is essential for maintaining healthy blood circulation in the pelvic region.