Concern is growing in Europe about alveolar echinococcosis (AE) with the increase in grassland rodent and red fox populations, intermediate and definitive hosts for Echinococcus multilocularis, respectively. The objective of this study was to assess the influence of rodent densities on human AE distribution. Spatial Poisson regression analyses were performed with geomorphologic features, landscape composition, climatic characteristics, and water vole density as independent variables. The outcome consisted of AE cases diagnosed over the period 1980-1992. High vole density yielded a 10-fold risk (relative risk [RR] = 10.34, 95% confidence interval [CI] = 2.78-38.39), and the first plateau (400-700 m altitude) compared with the plain (200-400 m) was associated with a large increase in risk (RR = 7.10, 95% CI = 1.30-38.63). These results confirm that human AE is strongly influenced by the densities of arvicolid species. Foxes feeding almost exclusively on grassland rodents when the latter expand could mediate this relation.