Occupational diseases (ODs) are defined as illnesses or symptoms that may be work-related but have not been recognized by social security systems. Since 2003, Santé publique France, in collaboration with the Occupational Health Inspection, has been responsible for the surveillance program for OSDs among French employees. This surveillance complements that conducted on recognized occupational diseases (ODs). The objective of OSD surveillance is to provide indicators on these conditions by specific employee populations, defined in particular by occupation or sector of activity. In participating regions, each participating occupational physician reports any MCP cases seen over a two-week period each semester. Socioprofessional data are also collected to calculate the prevalence of MCPs by sex, age, socioeconomic status, and sector of activity. Over the 2012–2018 period, the participation rate of occupational physicians declined, falling from 17% in 2012 to 13% in 2018, with the program’s geographic coverage remaining relatively stable. Among all MCPs observed during this period, the highest prevalences were for musculoskeletal disorders (MSDs) and psychological distress, followed by hearing disorders and irritations and allergies. Regardless of the year, the prevalence of MSDs was higher among women than among men. This prevalence remained relatively stable until 2015, then increased through 2018, from 3.1% to 4.4% for women and from 2.4% to 3.2% for men. A social gradient was observed for MSDs, with the highest prevalence among manual laborers. When adjusted for socio-occupational characteristics, the risk of MSDs was highest in the real estate sector for men, and in the accommodation and food services sector for women. MSDs were most often associated with biomechanical factors primarily related to work involving physical exertion, postural constraints, or repetitive movements. Nearly 70% of MSDs corresponded to a work-related injury. More than three-quarters of these MSDs had not been reported as work-related injuries, mainly due to insufficient diagnostic evaluation or a lack of awareness on the part of the employee. Psychological distress was reported two to three times more often among women than among men. Its prevalence increased gradually between 2012 and 2018 for both men and women, ranging over the period from 1.8% to 2.7% among men and from 3.5% to 6.2% among women, with a more marked increase since 2016. Unlike MSDs, an inverse social gradient was observed for psychological distress, with the prevalence of psychological distress being highest among managers and intermediate-level professionals. The risk of psychological distress was highest in the real estate sector for women and in the education sector for men. Organizational, relational, and ethical factors—primarily related to the functional organization of work, workplace relationships, job-related demands, and ethics—accounted for nearly all occupational exposure factors linked to psychological distress. This assessment, conducted over the 2012–2018 period, reinforces the need to continue this epidemiological surveillance system—unique in France—with a view, in particular, to better documenting the underreporting of occupational diseases and to helping guide occupational health and safety policies.