The mandatory reporting (DO) of mesotheliomas was established at the request of the Ministry of Health. It is included in the 2009–2013 Cancer Plan. It aims to address two objectives that complement those of the National Surveillance Program for Pleural Mesothelioma (PNSM) in 23 departments: 1 - strengthening epidemiological surveillance of mesotheliomas at all anatomical sites (pleura, peritoneum, etc.) throughout France (metropolitan and overseas territories); 2 - identifying cases with no known occupational exposure to asbestos, to improve understanding in three populations: women, people under 50, and non-pleural mesotheliomas (environmental exposure survey). The pilot phase took place in the first half of 2011 in six regions (Aquitaine, Île-de-France, Provence-Alpes-Côte d'Azur, Auvergne, Lorraine, Midi-Pyrénées), with the support of professional associations, regional cancer networks, and PNSM teams. The operational guidelines were developed in collaboration with the Regional Health Agencies and the Interregional Epidemiology Units. Participation by reporting physicians (pathologists, clinicians) was generally satisfactory, though with regional variations. This report presents the results of the pilot study, the 10 factors identified, and the recommended procedures for national rollout, validated by the Steering Committee and the High Council for Public Health. It is clear that a purely passive system without national coordination or active regional management is unlikely to succeed. The motivation of stakeholders must be sustained, with the support of professionals and institutions, through feedback demonstrating how this system benefits public health and patients. In certain regions, specific actions will be essential to implement this DO. (R.A.)