The aim of this study was to examine the origin of Cryphonectria hypovirus 1 (CHV1) which infects chestnut blight fungus, Cryphonectria parasitica. The genetic diversity of 39 CHV1 isolates from China, Japan and Italy was assessed by combining sequencing and restriction fragment length polymorphic (RFLP) experiments. Based on their partial sequences, 26 CHV1 isolates within 26 haplotypes were grouped into three subtypes. The 17 viruses from China were distributed between subtypes I and III, while all four of the isolates from Japan were subtype II. Of the five isolates from Italy, four were subtype I, and one (IT 192) was subtype III. Our analysis of the geographic distribution of the isolates indicated that all but one of the Chinese subtype III CHV1s are present in northern China; meanwhile all but three of the Chinese subtype I CHV1s are present in South China. Unlike in Europe where there is one predominant CHV1 subtype, our distribution analysis indicates that there has been gene flow between the populations in Asia. Cluster analysis based on the RFLP banding patterns showed that the viral isolates could be separated into four clusters. Most of the viral isolates (29 of 39, 74.4%) were grouped into one large cluster. Greater genetic diversity was observed among the CHV1s from China than among those from Japan and Italy. The Italian isolates were genetically more similar to the Japanese and South Chinese isolates than to the North Chinese isolates, indicating that CHV1 in Italy may have originated from Japan and/or South China.