Arteriovenous fistula of internal thoracic vessels is rare. We report a case of a 77-year-old woman with a fistula between the left internal thoracic artery and vein after a mediastinal needle biopsy through the anterior chest wall. The incidence of internal thoracic arteriovenous fistulas seems to be increasing because the number of cardiac and thoracic surgical procedures is increasing. It is important to consider an internal thoracic arteriovenous fistula as part of the differential diagnosis in patients with continuous murmur in the parasternal area.