Transient neonatal hypothyroidism (TH) is a state biochemically characterized by altered TSH and T4 values at screening and subsequently confirmed by serum analysis. TH can go or not go along with clinical manifestations of hypothyroidism and evolves to the normalization of the thyroid functional capacity independently of substitutive therapy. In addition to the complete TH the application of screening programs for congenital hypothyroidism has enable to acknowledge partial changes of the thyroid functional capacity in the neonatal age characterized by isolated anomalies of the individual hormonal parameters. Since the incidence of neonatal TH in Italy is remarkably high (the forms of complete TH being not less than 20% of the hypothyroidism cases diagnosed at the screening) we want to provide an overview of the latest acquisitions regarding TH. Finally the indications for treatment of the various forms of TH, a still controversial matter, are considered, in consideration of the primary role played by thyroid hormones on the development of central nervous system in the perinatal age.