Iodine is a constituent element of thyroid hormones which regulate many metabolic processes. Optimal daily intake of iodine for adults ranges between 150 and 250 μg, while during pregnancy and breastfeeding it should be around 250 μg. Mild iodine deficiency leads to thyroid growth and the occurrence of autonomous foci. Severe iodine deficiency, which is extremely rare in the developed countries, can cause hypothyroidism and impaired neurointellectual development in children. In iodine excess, an increased risk of autoimmune thyroid disease is observed, especially that of Hashimoto’s thyroiditis, which often leads to hypothyroidism. In patients with autonomous tissue, iodine excess may cause hyperthyroidism. For many years, Slovenia has been an area with mild iodine deficiency. Since 1999, when salt iodization was increased from 10 mg to 25 mg of potassium iodide per kg of salt, iodine supply reached the optimal level also for pregnant women and nursing mothers. However, inadequate iodine intake is possible in individuals consuming less salted or even uncooked unsalted vegetable food, or in those taking iodine preparations with consequently uncontrolled increase of iodine intake.