Congenital hypothyroidism is associated with increased incidence of congenital defects (15.6%), frequently involving the heart (5.8%). Only few studies have evaluated the association between congenital hypothyroidism and patent ductus arteriosus. We report on two term newborns affected by thyroid agenesis and patent ductus arteriosus that closed after starting L-thyroxine substitutive therapy. This association suggests a close relation between hypothyroidism and patent ductus arteriosus. Hypothyroidism should be considered in term infants with patent ductus arteriosus because thyroid hormone production is among the prerequisites for postnatal ductal closure.