[en] It appears that quantitative risk estimation for carcinogenesis will be used more and more in connection with case investigations or litigation involving individuals with a malignancy and a previous history of exposure to a carcinogen. There is some confusion as to how to handle the relevant probabilities. The problems involved are discussed. It is suggested that since the ICRP and the NCRP have now entered into quantitative risk estimation as applied to radiation protection, it would seem to be appropriate for these organizations to provide advice and guidance on appropriate methods for determining probabilities under different circumstances. (author)