Technical Abstract: The causal agent of Eutypa dieback of grape, Eutypa lata (Ascomycota), is a destructive disease worldwide. The pathogen has a broad host range, but causes severe symptoms on only a few cultivated hosts (e.g., apricot & grape). To decipher its cosmopolitan distribution, we examined the population genetic structure of 19 geographic samples from grape in four continental regions (Australia, California, Europe, So. Africa), based on analyses of 287 isolates genotyped with nine microsatellite markers. High genotypic diversity in all regions (Gd=0.9 to 1) and absence of multilocus linkage disequilibrium among loci supported the importance of sexual reproduction in all regions. The highest allelic richness (R’=3.9) and gene diversity (H=0.66 to 0.69) were in Europe, namely from coastal areas of the Mediterranean Sea. The lowest genetic diversity was in South Africa (R’=1.6 to 2.9; H=0.2 to 0.6). California, Australia and So. Africa, all of which had lower genetic diversity than Europe, were also characterized by demographic disequilibrium and, thus, may represent founding populations of E. lata. Low genetic differentiation among all samples (DEST=0.2, P=0.001; FST=0.03, P=0.001) suggests that gene flow among continents prevents differentiation. Human-mediated spread of E. lata, possibly via infected plant material (from grape or another host), may have resulted in its current global distribution. High genetic diversity of E. lata in European samples near the Mediterranean Sea may reflect this region’s more ancient history of viticulture.