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A 7 year old child with a genetic diagnosis of Williams-Beuren syndrome (microdeletion 7q11.23) had a ventricular septal defect, supravalvar and peripheral pulmonary artery stenosis, supravalvar aortic stenosis, and isolation of the left subclavian artery from the right aortic arch, originating from a patent ductus arteriosus. Cardiac catheterisation in infancy revealed systemic pressure in the central portion of the pulmonary arteries, and angiography showed systolic blood flow from the pulmonary to the left subclavian artery. At 7 years of age, peripheral pulmonary artery stenosis had decreased and mean pressure in the central PA was subsystemic. The left subclavian artery was now supplied by a retrograde perfused left vertebral artery with retrograde flow into the pulmonary arteries during diastole (pulmonary artery and subclavian artery steal) (a, aberrant left subclavian artery; s, stenoses of left and right superior lobe arteries). Right aortic arch with isolation of the left subclavian artery is the least common type of right arch. The embryologic development of this malformation can be explained by regression of the left aortic arch between the left common carotid and the left subclavian artery, as well as between the left subclavian artery and the descending aorta, with persistence of a small bridge of the left arch connecting the left ductus and the left subclavian artery. The diagnosis of this anomaly is of clinical importance because it can cause vertebrobasilar or left upper extremity ischaemia which is amenable to surgical treatment. We believe this is the first report of a right aortic arch with isolation of the left subclavian artery in a patient with Williams-Beuren syndrome.