Radioactive iodine isotopes may be released to air to a varying degree during accidents with nuclear reactors. Iodine tablets, taken before or shortly after such release, protect against intake of radioactive iodine isotopes, but not against other radionuclides. Iodine prophylaxis can be a relevant countermeasure in Norway and will be implemented according to recommendations from the Crisis Committee for Nuclear and Radiological Emergencies. The Chernobyl accident confirmed that the risk for radiogenic thyroid cancer is much higher for foetuses and children and adolescents under 18 years. An epidemiological study showed that intake of iodine tablets could reduce the risk for thyroid cancer by a factor of three. For children, the WHO has therefore recommended a 10 mGy avertable dose to the thyroid. The Norwegian Radiation Protection Authority acknowledge the WHO guidelines and advise that the first priority of all emergency preparedness planning for potential releases that can cause dispersion of radioactive iodine, should be given to the protection of pregnant and breast-feeding women, newborns and children under 18 years. Iodine tablets should be taken immediately (preferably not later than a few hours) in situations where inhalation of radioactive iodine may occur. It should be underlined that iodine prophylaxis is one of several emergency countermeasures; other measures are sheltering and evacuation. The latter two countermeasures will protect not only from intake of radioactive iodine, but also against other radionuclides that may be released. Based on the present risk assessment in Norway, iodine tablets have been distributed to the counties north of Salten. In addition, there is an emergency stockpile of iodine tablets in Oslo.