Following a pilot phase conducted in 2011 in six participating regions, mesothelioma was designated, by decree in January 2012, as the 31st notifiable disease (MDO). This project, led by the French Institute for Public Health Surveillance (InVS), was developed at the request of the Ministry of Health, with support from the National Cancer Institute (INCa) and various professional bodies and groups (French Society of Pathology (SFP), French-Speaking Society of Pulmonology (SPLF), Mesopath, National Network for Rare Peritoneal Tumors (Renape), Mesoclin, etc.). It is overseen by a Steering Committee (Copil). The mandatory reporting system is implemented at the regional level in collaboration with the Cire (InVS regional office), the Regional Health Agency (ARS), and the Regional Cancer Network (RRC). This DO contributes to the fight against asbestos-related cancers, which represent a major public health challenge. It is part of the 2009-2013 Cancer Plan. The DO is a comprehensive national system primarily focused on epidemiological knowledge, complementing the National Mesothelioma Surveillance Program (PMSM), which has been in operation since 1998 and is based on active, validated surveillance of all pleural mesotheliomas in 21 departments as of 2013. The objective of this DO is to monitor the situation of mesotheliomas throughout the country and to deepen our understanding of their causes, particularly environmental ones, in three targeted populations: pleural mesotheliomas in men under 50 and in women, and extrapleural mesotheliomas. This knowledge aims to enhance collective prevention efforts and medical-social recognition for the individual benefit of patients. The DO is not an expert assessment system and does not replace the occupational disease reporting system. This report presents the characteristics of the notifications received by the InVS and provides an estimate of the level of completeness achieved as of April 30, 2013, for cases diagnosed in 2012 (between 51% and 77% nationally). It highlights variations between regions. These results are very satisfactory for the first year of the DO but must be improved through comprehensive participation by physicians who diagnose mesothelioma. This report provides an update on the implementation of exposure surveys in nine pilot regions. (R.A.)