The accessory internal thoracic artery is a relatively large branch of the initial part of the internal thoracic artery, which was found in 4.54% of 22 cadavers studied in the Institute of Anatomy of the Medical School of Aristotle University of Thessaloniki. The course of this artery lies usually in the inner surface of the anterolateral thoracic wall and its diameter is sometimes almost equivalent to that of the main trunk of the internal thoracic artery. We think, that the knowledge of this arterial branch is essential for the thoracic surgeon during the preparation of the internal thoracic artery for coronary revascularization as well as for the surgeon during the placement of thoracic drainage for pneumothorax. Furthermore, it has to be kept in mind for the interpretation of angiographies of the subclavian artery.