The broad clinical utilization of the internal thoracic artery (ITA), including the role of its branches in supplying circulation to the sternum, requires explicit anatomic knowledge of this vessel. Fifty‐six ITAs (28 right, 28 left) were dissected from their point of origins after injection with a mixture of contrast medium and latex after perfusion with saline and immersion in 4% formaldehyde. All ITA branches were studied according to their course, size, and distribution within intercostal spaces with the aid of an operating microscope. The branches were divided in two main groups: proper (solitary) branches and common trunks. The proper branches consisted of four types: sternal, perforating, intercostal, and mediastinal. The four types of common trunks were: sternal/perforating, sternal/intercostal, perforating/intercostal, sternal/perforating/intercostal. Points of most frequent origin from main trunk of the vessel were established for each type. Mean external diameter of proper branches was 0.72 mm and common trunks was 1.06 mm. Mean length of common trunks was 3.0 mm. Those parameters (adequate diameter and length) allow for ligation of the common trunks close to the ITA so that their points of division can be preserved. This fact is crucial for creation of collateral blood supply to the sternum after bilateral ITA mobilizations. Clin. Anat. 12:307–314, 1999. © 1999 Wiley‐Liss, Inc.