The Chernobyl accident, the recent terrorists' attacks and constant threats, have all once again evoked the fear of a nuclear disaster, in Israel and worldwide. Iodine-131 is a major fission product of nuclear reactors and is highly likely to be released into the atmosphere in severe nuclear disasters. The radioiodine is released as a gas, easily spreads over large areas and is easily absorbed via the respiratory system. Iodine-131 emits gamma and beta radiation in high energies, and is readily absorbed by the thyroid which is a target organ for iodine. The resulting exposure to the thyroid might be very high. A sharp increase in thyroid cancer incidence in children was observed following the Chernobyl accident. This article reviews the medical knowledge about strategies and medications aimed at minimizing the absorption of radioiodine into the thyroid. In addition to regular safety means such as sheltering, restriction of locally produced food products and relocation of the population, the best prophylaxis against thyroid exposure is overloading the gland with stable iodine (as potassium iodide), as soon as possible. Recently, the Israeli government decided to distribute Potassium Iodide tablets to the population in the vicinity of the two nuclear research centers in the country. When this treatment is contraindicated, iodine free thionamides or potassium perchlorate are suggested.