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Introduction: This study was designed to describe the difficulties of epidemiological follow-up of employees by occupational health services.Methods: This study was based on two transverse studies conducted by the Pays de la Loire musculoskeletal disorders (MSD) surveillance network. Eighty-three occupational health physicians included 3,710 employees between 2002 and 2005 and had to review them between 2007 and 2009. Thirteen of these physicians changed jobs and 7 changed geographical sector in the same occupational health service.Results: Another 94 physicians were contacted and 85 agreed to participate in the network. The follow-up rate was 43% : 1,044 employees were reviewed by the physician who saw them on inclusion and 567 employees were reviewed by another physician of the network. The other employees were distributed as follows : 25% were lost to follow-up and their occupational status remained unknown ; 23% were still employed with an identified occupational health physician but had not attended a medical visit during the follow-up study ; 5% had left the occupational health surveillance system. Only 23 employees refused to participate in the follow-up and 105 employees had a physician who refused to participate.Discussion: There is therefore a considerable mobility of occupational health physicians, which interfered with follow-up despite their good mobilization and a high percentage of employee are lost to follow-up after having left their jobs. More appropriate systems must be set up to follow populations of employees, such as new collaborations with general practitioners.