Approaches to and results for the estimation of healths risks from indoor exposure to radon and its daughter products are discussed. Particular weight is given to the derivation of exposure-time-effect relationships using a modified proportional hazard model which has been adapted to account for relevant epidemiological data. The results of this analysis indicate that about (10 ± 5) % of the lung cancer rate observed in the general public might be correlated to the enhanced exposure to radon daughters in dwellings (at 10 - 20 Bq/m3 (Rn-eq) and in outdoor air. A chronic exposure to indoor Rn-levels at home of about 300 - 500 Bq/m3 (Rn-eq) might possibly double the normal lung cancer rates. The relative fractions of radiogenic lung cancer rates might be nearly the same for smokers and non-smokers, and for men and women.