Neonatal screening for congenital hypothyroidism (CH) began in Italy in 1977 and then progressively developed covering 97% of live births in 1992. The National Register of infants with congenital hypothyroidism was established in 1987 as a project of the Health Ministry and is coordinated by the Italian Institute of Health. The aim of the Register is to provide disease surveillance, to monitor the efficiency and effectiveness of neonatal screening and to allow the identification of possible etiological risk factors in congenital hypothyroidism. The results of the Register provided valuable epidemiological informations about congenital hypothyroidism in Italy and evidenced several areas in whom an increased incidence probably caused by iodine deficiency was observed. Discussion of Register data during annual national meetings has allowed an improvement of the screening program with particular regard to the beginning of therapy with L-thyroxine and its dose. Because of the wide spectrum of collected information, the National Register represents a useful tool for developing of collaborative studies concerning some aspects of CH not yet completely elucidated.