 The children are part of a cohort study that recruited their mothers before they were conceived. Women registered with a general practitioner in the Southampton area were recruited at ages 20-34 years when they were not pregnant. Those who subsequently became pregnant were followed through the pregnancy and then the children are being followed-up. This study focuses on iodine measures from the preconception recruitment and the follow-up in their homes of the children aged 6-7 years. 