As a part of our effort in quantitative risk analysis of food-borne diseases, we carried out an epidemiologic study to estimate the prevalence of multidrug resistant (MDR) Salmonella in dairy herds situated in western France. The study population consisted of 489 farms in the region and manure or slurry was sampled from these operations and tested for the Salmonella spp. All strains isolated during the study were serotyped and tested for their antimicrobial susceptibility. Salmonella spp. was isolated from 8.1% (95% confidence interval (CI 95%): 4.5-13.3%) of the sampled herds. The herd prevalence of MDR Salmonella among the sampled herds was 1.9% (CI 95%: 0.5-5.4%). Spatial statistics were used to check for sampling representativeness and to determine if infected herds were clustered spatially.