Introduction - One of the main objectives of the mandatory reporting (MR) of mesotheliomas is to strengthen the surveillance of mesotheliomas (across all anatomical sites and throughout the country). The objective of this study is to provide an overview of this MR system in terms of the number of reports, the characteristics of reported cases, the types of reporting physicians, and the completeness of the data. Materials and Methods - Since 2012, all physicians (pathologists and clinicians) practicing in France who diagnose mesothelioma must report it to the Regional Health Agency in their area of practice. Completeness was estimated for pleural mesotheliomas by comparison with data from the National Pleural Mesothelioma Surveillance Program (PNSM). Results - 4,546 cases of mesothelioma diagnosed between 2012 and 2018 were reported as of October 10, 2019. These cases were reported by a pathologist (77%) and/or a clinician (55%). The tumor was located in the pleura (89%), the peritoneum (8%), and, in 3% of cases, at other sites. The number of reported cases increased between 2014 and 2015, then decreased through 2018. The average completeness rate for pleural mesotheliomas in the departments covered by the PNSM was 50%, with significant regional disparities. Conclusion - The mesothelioma registry is functional and informative but still insufficiently comprehensive. It is crucial to improve the completeness of this registry, which will play an essential role within the National Mesothelioma Surveillance System (DNSM).