Introduction: The objective of this study is to describe the challenges of conducting epidemiological follow-up of employees within occupational health services (OHS). Methods: The study is based on two cross-sectional studies from the Musculoskeletal Disorders (MSD) Surveillance Network in the Pays de la Loire region. Between 2002 and 2005, 83 occupational physicians enrolled 3,710 employees; they were scheduled to follow up with them between 2007 and 2009. Of these, 13 had left their department and 7 had moved to a different geographic area within the same OSH service. Results: Of the 94 additional physicians contacted, 85 agreed to participate in the network. The follow-up rate was 43%: 1,044 employees were re-examined by their original physician, while 567 employees were re-examined by another physician in the network. The remaining employees were divided as follows: 25% were lost to follow-up with their employment status unknown; 23% were still employed with an identified occupational physician but did not attend a medical examination during the follow-up study; 5% had been removed from the occupational health surveillance system. Only 23 employees refused to participate in the follow-up, and 105 had a physician who refused to participate. Discussion: There is, therefore, on the one hand, high turnover among occupational physicians, which slowed down the follow-up despite their strong commitment, and on the other hand, a high percentage of employees who were lost to follow-up after leaving their jobs. More appropriate mechanisms must be put in place to monitor a population of employees, such as new collaborations with general practitioners. (R.A.)