Genetic variation within Gremmeniella abietina var. abietina was studied using the Random Amplified Microsatellite-technique (RAMS). Ninety-three isolates were investigated, originating mostly from Finland, but also from Canada, U.S.A., Japan, Norway, Italy, Iceland and Sweden. Four banding pattern types were observed corresponding to the present division of this species in Asian, North American and two types of European races. Furthermore, an additional banding pattern was also observed. Intraracial variation was observed within all races, the North American one being the most polymorphic. Isolates of the large tree type (LTT) Gremmeniella from North America, Italy and Iceland contained RAMS alleles not observed in Finland, Sweden or Norway. Therefore, the isolates of LTT Gremmeniella should not be transported even within the area of its natural occurrence.