A 15-year-old girl presented with upper extremity hypertension and continuous precordial murmur. Arteriography revealed aortic coarctation proximal to the origin of the left subclavian artery. An anomalous artery originated from the aortic arch, between the left common carotid artery and the stenosis. It ascended cranially and filled an angiomatous vascular formation on the left side of the neck. The "angioma" drained into the left subclavian artery. The embryological explanation of the described anomaly is difficult, but probably related to hemodynamic alterations following the prestenotic increase in blood pressure. This may have impaired the obliteration of cervical intersegmental arteries, resulting in the persistence of one of the first three intersegmental arteries as the anomalous branch of the aortic arch. The angiomatous vascular formation in the neck could be the consequence of altered development of anastomoses between the muscular twigs of both vertebral and deep cervical artery. The vessel draining the vascular formation was probably the thyrocervical trunk. Since there were no overt collateral channels or signs of left ventricular hypertrophy by electrocardiography and echocardiography, it seems that the aberrant collateral flow was hemodynamically significant and reduced the afterload on the myocardium. Although the pattern of collateral flow in our case might be considered extremely rare, it is important in preoperative planning and interpretation of imaging studies.