Newborn screening for congenital hypothyroidism (CH) has become routine in Italy. It provided new information regarding the epidemiology, diagnosis and treatment of CH infants and allowed to identify transient disorders of thyroid function in infancy. In fact, when the permanence of hypothyroidism has not been established in the newborn period, a confirmation of the diagnosis at 2-3 years of life should be performed. In this study results regarding the diagnosis reevaluation performed in 23 out of 184 CH children followed at the follow-up center for CH of the University of Rome "La Sapienza", are reported. Eleven of 23 reevaluated children had transient hypothyroidism (TH) and permanent CH was confirmed in the others. Four of the 11 TH children had law gestational age at birth, 1 had high antithyroid peroxidase titre due to maternal autoimmune thyroiditis and 2 were resident in iodine deficient areas. Our results show the importance of diagnosis reevaluation to identify transient disorders of thyroid function in infancy and confirm the role of neonatal, maternal and environmental factors in the etiopathogenesis of TH.