The great saphenous vein is a large vessel running near the inside surface of the leg from the ankle to the groin. It arises from the dorsal venous arch in the top (dorsum) of the foot and drains into the femoral vein.

From the foot, it travels through the back of the knee area and ascends through a triangular opening in the thigh that is formed by two muscles and a ligament. Before reaching the femoral vein, it collects blood from several smaller veins, including the superficial gastric, superficial circumflex iliac, and superficial pudental.

The purpose of the great vein is delivery of blood from the ankle, lower leg, and thigh to the femoral vein, which is the main deep vein for the leg. Along its length are 10 to 20 one-way valves that keep the blood from flowing back toward the foot. Varicose veins occur when one or more valves stop working, creating distended areas where blood has backed up into smaller veins just under the surface of the skin.

The great saphenous vein is sometimes stripped out of the leg to eliminate varicose veins. It is also used as the source of grafts in coronary bypass surgery.