The proposed study will establish a cohort with individual radiation dose estimates from combined internal and external sources of irradiation. This unique cohort will add important new information on adverse health effects following prenatal and postnatal exposure to radioiodines and radiocesium, for which available epidemiological data are scant. Such data could contribute valuable data for development of better radiation and medical countermeasures to protect pregnant women and young children who could be potentially exposed to harmful levels of ionizing radiation through radiological and nuclear incidents.