The right and left brachiocephalic veins are located immediately posterior to the thymus. Each of these veins are formed by the internal jugular and subclavian veins and together they meet to form the superior vena cava.

The right brachiocephalic vein begins behind the medial end of the right clavicle, descends vertically, forming the superior vena cava, when it is joined by the left brachiocephalic vein. Its major venous tributaries are: vertebral, first posterior intercostal, and internal thoracic veins. It may also receive the inferior thyroid and thymic veins.

The left brachiocephalic vein begins behind the medial end of the left clavicle, passes to the right, moving in a slightly inferior direction, then crosses the midline (behind the manubrium in the adult) and joins with the right brachiocephalic vein to form the superior vena cava posterior to the lower edge of the first costal cartilage close to the right sternal border. The venous tributaries to the left brachiocephalic vein include: the vertebral, first posterior intercostal, left superior intercostal, inferior thyroid, and internal thoracic veins. It may also receive thymic and pericardial veins.