Biogeographic patterns and large-scale genetic structure have been little studied in ectomycorrhizal fungi, despite the ecological and economic importance of ectomycorrhizal symbioses. We coupled population genetics and phylogenetic approaches to understand spatial structure in fungal populations on a continental scale. Using 9 microsatellite markers, we characterised gene flow among 16 populations of the widespread ectomycorrhizal basidiomycete Laccaria amethystina over Europe (over 2900km). We also widened our scope to two additional populations from Japan (104 km away), and compared them with European populations through microsatellite markers and multi-locus phylogenies, using 3 nuclear genes (NAR, G6PD and ribosomal DNA) and two mitochondrial ribosomal genes. European L. amethystina populations displayed limited differentiation (average FST=0.041) and very weak isolation by distance. This panmictic European pattern may result from effective aerial dispersal of spores, high genetic diversity in populations, and mutualistic interactions with multiple hosts that all facilitate migration. The multi-locus phylogeny based on nuclear genes confirmed that Japanese and European specimens were closely related but clustered on a geographical basis. By using microsatellite markers, we found that Japanese populations were strongly differentiated from the European populations (FST=0.416), more than expected by extrapolating the European pattern of isolation by distance. Population structure analyses clearly separated the populations into two clusters, European and Japanese clusters. We discuss the possibility of isolation by distance in a continuous population (considering some evidence for a ring species over the Northern Hemisphere) versus an allopatric speciation over Eurasia, making L. amethystina a promising model of intercontinental species for future studies.