Objective. - To estimate the seroprevalence of Lyme disease and tick-borne encephalitis (TBE) among forestry workers. Methods. - Professionals exposed to tick bites in eastern France were interviewed by occupational physicians from the Mutualité Sociale Agricole (MSA) regarding their sociodemographic characteristics, occupational activity, most recent tick bite, clinical history, and preventive measures. A blood sample was collected for serological testing. Results. - Among the 2,975 subjects included, the observed seroprevalence was 14.1% for Lyme disease and 3.4% for TBE. Age, occupational activity, and place of residence significantly influenced serological status with regard to Lyme disease. The seroprevalence among loggers (17.5%) was significantly higher than that of other occupational categories (p < 0.001). Seroprevalence rates in Alsace (26.9%) and Lorraine (16.5%) were significantly higher than those in the other regions studied (p < 0.001 and p < 0.01, respectively). The seroprevalence of TBE was significantly higher in Alsace (5.5%; p < 0.001). Seroprevalence rates varied by forest massif for both diseases. Multivariate analysis of prevention practices revealed three types of behavior: "rigorous," "partial," or "absent" protection. Conclusion. - These results do not alter the current vaccination recommendations for TBE. They underscore the importance of information on these diseases and the need for further studies on microbial ecology and the identification of risk factors. (R.A.)