The intercostal veins are paired vessels that run together with the intercostal nerves and arteries in the intercostal spaces. They go above the intercostal arteries and nerves and are the highest-located structures within the subcostal grooves. The intercostal veins can be classified into two groups - anterior and posterior intercostal veins. Both groups anastomose with each other. Overall, the intercostal veins drain the thoracic walls and carry blood to various vessels described below.