Radon is a naturally occurring radioactive gas that accumulates in poorly ventilated homes. It is a known lung carcinogen in humans. The exposure of the entire French population to widely varying concentrations of radon raises questions about its impact on public health. To provide insights, this study proposes a predictive assessment of the health impact of domestic radon exposure in metropolitan France. Using all available data on the relationship between exposure and lung cancer risk, as well as estimates of exposure among the French population, this study is based on a quantitative health risk assessment approach; it includes an analysis of variability and uncertainties that allows for the calculation of an uncertainty interval around the prediction. The annual number of lung cancer deaths attributable to indoor radon exposure in metropolitan France ranges from 1,234 (90% uncertainty interval:593–2,156) to 2,913 (90% uncertainty interval: 2,763–3,221) depending on the exposure-response relationships used. These figures show that indoor radon exposure is a major public health issue in France. (R.A.)