Radon is a natural radioactive gas, with worldwide distribution, deriving from uranium decay products, which can be inhaled, weather in mining condition (extraction and management of uranium ores) or in domestic condition (in some high risk homes or geographic areas). The main epidemiologic studies on uranium mining workers have all confirmed an excess in relative risk of primary lung cancer. Epidemiologic studies on indoor exposure suggest a role of radon in the genesis of a certain number of primary lung cancer, although these results remain controversial and need to be confirmed. An overview of the main actual problems related to this bronchial carcinogen is presented in this paper.