A certain connection exists between the level of radon in the air and diseases of the human respiratory system. The prersent research evaluates the risk of disease incidence with oncologic lung illnesses and mortality rate from them on the account of exposure during the inhalement of internally in-built radon by the population in Rivne city dwellings. We measured radon in 2011-2016 and used radonometer «Alfarad Plus». The method proposed by Covello and Merkhofer (1993) and NRC (1983) is used. In accordance with it, the assessment of mortality rate of city inhabitants from lung cancer due to internal exposure to radon was carried out in four stages. This, in particular, is the identification of population, the analysis and selection of the most optimal dependence of «dose-effect», the direct evaluation of radon influence on population and the calculated risk of lung cancer. The measurement of radon concentration in premises in Rivne testify its substantial variability. The average geometric value of VA for basement premises amounts to 365 Bk/cub.m and for semi-basement premises-161 Bk/cub.m. The prognosticated maximum possible value of VA in buildings by results of our measurements is assessed as 1.420 Bk/cub.m. Thus, the calculated expected shortening of life duration for population of Rivne by different models of DDE constitutes from 1.2 to 4.0 years for the whole population and from 2.5 to 7.41 years for those share of population who smokes.