An increase in the incidence of thyroid cancer has been observed in the general population in France for more than 20 years. The Chernobyl accident on April 26, 1986, was responsible for an epidemic of thyroid cancer in the countries most exposed (Belarus, Ukraine, and Russia). Exposure to iodine-131 released during the accident played a key role in the onset of these cases, but other factors are also suspected. In France, the increase in the incidence of thyroid cancer in the general population is often perceived by the public and physicians as one of the possible consequences of this accident, although it began well before 1986. Consequently, in January 2000, the Directorate General for Health asked the Institute for Nuclear Protection and Safety and theNational Institute for Health Surveillance to conduct an assessment of the health consequences of this accident in France and to formulate recommendations on the epidemiological approaches that should be undertaken to identify the potential impact of this accident on the incidence of thyroid cancer. This work led to the publication on December 15, 2000, of a report, two elements of which are presented in this article: an assessment of the risk of thyroid cancer potentially linked to fallout from the Chernobyl accident in France and a discussion of the relevance of possible epidemiological approaches.