Many countries in the world are inhabited by populations suffering from iodine deficiency. These populations are affected by serious diseases directly related to iodine deficiency. Iodized oil (Lipiodol UF® or Oriodol®) is routinely used orally or intramuscularly to treat these populations, including pregnant women. The experiments of the present study in gravid or lactating rabbits show that there is transplacental transfer of iodine and secretion of iodine in milk after administration of iodized oil and consequently an accumulation of iodine in the thyroid glands of the mother, the fetus and the neonate. The advantages of treating pregnant women with iodized oil in the populations concerned is thus confirmed. The oral route can be substituted by the intramuscular route.