Abstract: Strawberry powdery mildew, caused by Podosphaera aphanis, is one of the most important diseases worldwide. Mildew lesions were sampled from a number of cultivars at several sites in the UK; a limited number of lesions was also sampled from China, the USA, Italy and Israel. SSR markers were developed and used to genotype sampled isolates for determining population variability; the ITS region of 20 samples selected from different countries was sequenced. Both SSR and ITS data indicated that there were significant differences between samples from the USA and the other countries. In the UK, there was significant population differentiation between mildew samples from different cultivars at the same sites, or between mildew samples from the same cultivar at different sites.