The main stages of and principles of methodology of assessment of a carcinogenic risk from exposure to environmental factors are considered. The carcinogenic risks of exposure to MAC of in the ambient air of the populated areas, in the reservoir water, and in the air of a working zone were calculated by using the carcinogenic potential. Analyzing the data obtained has indicated that a great variety of potential carcinogens presents a high risk even if the hygienic standards approved now are followed. The methodological and organization aspects of the use of the procedure for assessing carcinogenic risks in Russia are discussed.