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The risk of thyroid cancer from reactor accidents has long been a salient factor in the analysis of nuclear reactor safety. This risk arises largely from the abundance of iodine-131 in the fission product inventory. Iodine disperses widely if released into the atmosphere and could enter the human food-chain, particularly through consumption of contaminated cows' milk. Iodine entering the human body concentrates in the thyroid gland, which becomes the most highly irradiated organ or tissue. However, thyroid cancer is rarely fatal even when it is not diagnosed and treated. Although it is likely to be the greatest risk of radiation induced cancer, it may not constitute the greatest risk of death. The objective of this paper is to place this risk into its proper perspective. Published predictions and the observed consequences of reactor accidents are considered. In the Chernobyl accident, an increase in the incidence of thyroid cancer in children occurred more rapidly than expected and several hundred identified cases are more likely to have been caused by radiation from Chernobyl than from any other cause. Apart from the increased incidence of thyroid cancer, no other physical effect of radiation exposure on public health is likely to be discernible from this accident or from any other reactor accident that might occur. [ABSTRACT FROM AUTHOR]