Study objective: Radon exposure poses a major environmental health risk, yet remains largely unknown to the general public. In particular, it is the second leading cause of lung cancer after smoking. The objective of this retrospective cross-sectional survey was to assess the current state of knowledge regarding radon itself and as a risk factor, and to examine the various social factors associated with it. Materials and methods: The 2010 Cancer Barometer surveyed the French population. The survey was conducted from April 3, 2010, to August 7, 2010, using telephone and computer-assisted data collection, based on a two-stage random sample of 3,359 individuals aged 15 to 75. Results: Radon remained largely unknown to the general public, including in departments identified as being at risk. Among people aged 15 to 75, only one in five knew that radon is a naturally occurring gas from the ground. This awareness was more common among people living in a department at risk from radon, among men, and increased with age, educational attainment, and income level. When people were exposed to radon, few considered addressing the issue through home renovations. Conclusion: The success of prevention efforts requires the commitment and collaboration of various national and local stakeholders involved in this issue. To enhance their impact on lung cancer prevention, it might be more effective to combine these efforts with tobacco prevention messages. (R.A.)