A brief survey presents effective doses from radiodiagnostic and nuclear medicine medical examinations, representing the basis of estimating lifetime radiation risk of stochastic effect of ionizing radiation. Two suggestions published in literature are given for the categorization of imaging methods according to effective dose and radiation risk. The radiation risk of developing fatal malignant tumors due to irradiation may reach, in the CT examination of children, the values of 1:1000 or higher as a result of combination of age dependence of radiation risk related to the unit of effective dose and the age dependence of effective dose. In comparing the radiation risk with non-radiation risks of other methods of examination in medicine and the risk of other human activities and life environment it is important to bear in mind a hypothetical character of radiation risk, which may become manifest in humans after a long period of time elapsing from irradiation during diagnostic examinations.

        Key words: effective dose – radiation risk – age dependence – radiodiagnostics – nuclear medicine