In 2000, the Ile-de-France Regional Health Observatory conducted a survey of the general adult population on perceptions of tobacco and its risks. This article presents one aspect of that survey, focusing on perceptions of the risk of lung cancer. The objective is to demonstrate the gap between knowledge of the risk and the perception of that risk for oneself, that is, the discrepancy between general knowledge and individual perception. Among the respondents, the following findings can be identified: On the one hand, the health consequences of tobacco use are better understood by nonsmokers than by smokers. On the other hand, in addition to “not smoking,” other measures—which are, in fact, marginal in terms of their effectiveness—are considered effective in preventing lung cancer. The vast majority of smokers not only believe they benefit from personal exemptions that protect them from the risks associated with their tobacco use, but also greatly underestimate the health benefits of quitting smoking.