The underreporting rate of musculoskeletal disorders (MSDs) as occupational diseases (ODs) refers to the proportion of MSDs that were not reported as ODs among all work-related MSDs affecting employees and meeting the criteria for an occupational disease. In 2016–2017 and 2018–2019, the underreporting rate ranged from 50% to 75% for all MSDs considered (shoulder, elbow, lumbar spine, carpal tunnel syndrome (CTS)), regardless of the employees’ gender. Despite a one-time decline in 2013, underreporting of shoulder MSDs remained relatively stable between 2009 and 2016–2017, ranging from 59% to 65%, before rising to 72% in 2018–2019. This increase toward the end of the period was particularly pronounced among women. Underreporting of musculoskeletal disorders (MSDs) was relatively stable between 2009 and 2019 (between 55% and 60%), with the exception of a sharp decrease in 2015 (43%). Underreporting of MSDs of the elbow and lumbar spine remained relatively stable throughout the 2009–2019 period, ranging from 60% to 70% for the elbow and 50% to 60% for the lumbar spine. The main reasons for underreporting were the employee’s lack of familiarity with the process, an inadequate diagnostic assessment, and the employee’s refusal; this refusal was due in the majority of cases to fear of job loss. The underreporting of MSDs, although difficult to assess, therefore remains a significant phenomenon, underscoring the importance of continuing to improve accurate information on work-related accidents and occupational diseases (AT-MP) for workers, employers, and physicians. Furthermore, in 2024, these results informed the work of the Commission established by Article L.176-2 of the Social Security Code, which is tasked in particular with estimating the cost of unreported occupational diseases.