Iodine is the essential constituent of thyroid hormones. Iodine deficiency disorders, ranging from endemic goiter to cretinism, result from low dietary intake of iodine. The fetus and the newborn are more sensitive than adults to a reduced environmental iodine supply, and in iodine-deficient areas, transient neonatal hypothyroidism is frequently observed. This transient thyroid failure may be associated with neonatal goiter. Border-line elevated neonatal TSH levels frequently occur in iodine deficient areas, and result in a higher recalling rate in the screening for congenital hypothyroidism. Iodine prophylaxis is highly effective in preventing the development of iodine deficiency disorders including transient neonatal hypothyroidism. Since iodine prophylaxis in Italy is inadequate, variable degrees of iodine deficiency are still present all-over the Country, and are responsible of a higher incidence of transient neonatal hypothyroidism or hyperthyrotropinemia. Educational programs for the general population, health professionals, and decision makers are essential for a successful iodine prophylaxis. Elimination of iodine deficiency by the year 2000 has been recently pledged by WHO/UNICEF. This goal is feasible if pursued with sufficient vigor and resources.