A total of 134 Cryphonectria parasitica isolates were sampled from the two most important chestnut-growing areas of Turkey. Isolates were screened for vegetative compatibility (vc) by pairing them with the 64 EU testers. All isolates belonged to one vegetative compatibility type, which was compatible with the vc type EU-1. Twenty-four randomly selected isolates were screened for mating type, using a PCR-based method. We found isolates of the two mating types, although MAT-1 isolates prevailed. The skewed ratio of the two mating types is an indicator of the lack or limited sexual reproduction of the fungus in nature. The absence of diversity for vegetative incompatibility types indicates that the introduction of the pathogen has been seldom, and has probably been followed by a strong founder effect. In addition, all isolates were screened for Cryphonectria hypovirus 1 (CHV1) infection, visually assessing the colour of the mycelium grown on PDA. Nineteen out of 134 isolates were virus infected. The presence of virus-infected isolates, coupled with the characteristics of the C. parasitica population, indicates that there is a great potential in Turkey for successfully controlling chestnut blight biologically.