Facts and rumors have circulated regarding the potential health consequences of the 1986 Chernobyl accident. Thyroid cancers, in particular, have been a topic of debate. Were they on the rise? If so, to what extent could the Chernobyl accident have been the cause? In response to these questions, the Directorate General for Health (DGS) mobilized its expert bodies to gather solid epidemiological data. Consequently, the French Institute for Public Health Surveillance (InVS) was tasked with conducting epidemiological surveillance of thyroid cancers linked to ionizing radiation. We now have the initial results of this study, which is also part of a new national epidemiological surveillance initiative for cancers linked to the environment. (Introduction)