Superior thyroid artery is the first anterior branch of external carotid artery. It is intimately related to external laryngeal nerve. The superior thyroid artery supplies upper one third of thyroid lobe and the upper half of isthmus. The inferior thyroid artery is a branch of thyro cervical trunk, which arises from subclavian artery. Its terminal part is related to recurrent laryngeal nerve. The inferior thyroid artery mainly supplies lower 2/3rd' of thyroid lobe and lower half of isthmus, trachea, parathyroid and thymus.