In a national sample of school aged children (n=990), pregnant women (n=700) and women of reproductive age (n=700) urinary iodine will be determined in order to assess iodine nutrition in Switzerland. In addition, in both groups of women a blood sample will be taken for the determination of thyroid hormones, iron- and folate status. Questionnaires will be used for the determination of dietary iodine and salt intake as well as sociodemographic parameters.