Thyroid cancers are very rare before the age of 15: they account for less than 1% of childhood cancers. An analysis of cases recorded from 1978 to 1997 by French cancer registries (general, pediatric, and specialized thyroid cancer registries) shows an incidence ranging from 0.56 to 1.77 per million, with significant variations depending on the registry and the year. Consequently, nationwide coverage is necessary; which must be provided by the National Registry of Solid Tumors in Children (RNTSE), although its methodology must be adapted. Indeed, since these are not specifically pediatric tumors, they are rarely managed by pediatric oncology teams but rather follow the same care pathways as adults (ENT, endocrinology, and surgery departments). Furthermore, as part of monitoring the potential long-term effects of the Chernobyl accident in France and assuming a latency period of at least 5 years between exposure and the onset of cancer, consideration should be given to extending data collection to adolescents aged 15 to 19. The objective of this study is to assess the feasibility of establishing a national surveillance system for these thyroid cancers and of extending the registry to the 15–19 age group. (Introduction)