Indoor radon exposure is the second most important risk factor for lung cancer incidence on human. The purpose of this study was to assess the status of the knowledge of radon gas in the general population and high school students, in the metropolitan area of Naples. A survey was planned in order to obtain data on both public knowledge of radon gas and its health effects. The results on 6705 collected questionnaires showed that a similar percentage of respondents asserted to know radon gas, 31% and 38% in general and student population, respectively. This study demonstrate that actual educational programs have to be enhanced in order to provide the spread of the radon knowledge and the awareness of the exposure risk.