Chestnut blight is a significant disease in Turkey. A survey of the chestnut-growing areas in Turkey was therefore conducted and 324 Cryphonectria parasitica isolates were obtained from bark samples. Among these isolates, 14 had a white phenotype and were probably hypovirulent. The presence of dsRNA was confirmed for seven of these isolates. The isolates fall into two vegetative compatibility (vc) types, EU-1 and EU-12. Seven hypovirulent isolates could convert all the virulent isolates assigned to the vc type EU-1. Pathogenicity tests were performed on young chestnut plants. The hypovirulent isolates caused only small cankers that healed in a short time. Similarly double inoculations with virulent and hypovirulent strains resulted in small cankers that healed and formed callus tissue. It is concluded that controlling the chestnut blight with hypovirulent strains will be feasible in Turkey.