The phylogenetic relationships of the stem rot pathogens Sclerotium rolfsii and S. delphinii were examined, based on their rDNA ITS sequences. The ITS regions were cloned and sequenced to identify three distinct ITS types: r-1, r-2, and r-3. Two different ITS types exist within S. rolfsii and S. delphinii strains. Japanese strains and one strain of S. rolfsii from the USA contain types r-1 and r-2, whereas another strain from the USA and one from Chile have only one ITS type, r-2. S. delphinii strains have types r-1 and r-3. We discuss the implications of the common presence of ITS type r-1 for the taxonomy and evolution of this species complex.