Increasing attention is being paid to the health risks of indoor radon exposure and its impact on the general population. In regions where radon is a potential issue, an accurate assessment of this impact is a prerequisite for targeting effective risk prevention policies. Here we present a study of indoor radon measurements, taken in a 450-dwelling sample in a French region of high radon potential (Franche-Comté) to assess exposure levels and determine the influence of dwelling characteristics and lifestyle on radon concentrations. The geometric mean of radon concentration was 73.9 Bq/m3 and 23.3% of homes had measurements above 200 Bq/m3. Around 25% of the variation in radon concentrations was explained by a multivariate regression model that included 6 basic and easy-to-collect variables: local geology, type of dwelling, date of construction, what lies beneath the dwelling, presence or absence of mechanical ventilation, and daily duration of open windows.