Supravalvar aortic stenosis is the most frequent operation required for Williams syndrome; however, coarctation repair is more common in patients requiring surgery in the first few months of life. We report on a child with Williams syndrome in whom extensive reoperation was required 5 months after neonatal aortic coarctation repair. A composite left subclavian artery flap and allograft patch aortoplasty of the aortic arch and descending aorta was performed through a left thoracotomy using cardiopulmonary bypass and circulatory arrest. Detailed anatomic evaluation of the aortic arch and descending aorta is recommended before initial coarctation repair in neonates with Williams syndrome.