Purpose of the study. - During the COVID-19 pandemic, the changes in working conditions, the fear of being contaminated at the work place and job insecurity can have a significant impact on the mental health of employees. The objective of this study was to measure the impact of the pandemic on the mental health of employees under follow-up in an occupational health service and to identify the factors associated with stress and fear at work. Method. - An anonymous and confidential questionnaire was offered to employees coming to occupational health visit in early October and November 2020. Results. - Among the employees, 1797 responded. Nearly 40% had manifestations of anxiety disorders and 20% had depressive signs. From the beginning of the crisis, almost a third of employees were more stressed than before and 21% happened to be afraid at work. Being more stressed at work was associated with gender, number of employees, seniority, working in the health sector, feeling affected by SARS-COV2, being at risk of severe covid-19, feeling exposed to SARS-COV2 at work, feeling insecure at work and having difficulties to apply barrier measures. The multivariate model analysis looking at factors associated to fear at work had similar findings. Conclusion. - This study confirms and quantifies the importance of stress, feelings of insecurity and tensions at work. These results emphasized the role of an occupational health service in the face of a health crisis to best support employees and employers.