Iodine is an essential component of the thyroid hormones thyroxine (T4) and triiodothyronine (T3) which play a crucial role in brain and neurological development. The ideal dietary allowance of iodine recommended by World Health Organisation (WHO) is 150 μg of iodine per day which increases to 200250 μg/day in pregnancy. Severe iodine deficiency may be associated with impairment in the psycho-neurological outcome in the progeny because both mother and offspring are exposed to iodine deficiency during gestation (and the postnatal period). Controlled studies performed in iodine-deficient regions have confirmed that iodine supplementation eliminated new cases of cretinism, reduced infant mortality and improved cognitive function in the general population. Even mild iodine deficiency is thought to lead to reductions of 1015 in the intelligence quotient (IQ) points. Many people are still deficient in iodine, despite major national and international efforts to increase iodine intake, primarily through the voluntary or mandatory iodisation of salt. The WHO estimates that two billion people, including 285 million school-age children, still have iodine deficiency, defined as a urinary iodine (UI) excretion of less than 100 μg/l. Recent epidemiological data suggest that iodine deficiency may also now be an emerging issue in industrialised countries such as the UK, previously thought of as iodine-sufficient. International efforts to control iodine deficiency are slowing, and reaching the third of the worldwide population that remains deficient poses major challenges.