Botr yosphaeria stevensii frequently has been associated with dieback and canker diseases of oak, mainly in the western Mediterranean area but more rarely in other regions. The species concept of B. stevensii has been unclear, and it is possible that some collections were identified incorrectly. A collection of fungal strains isolated from diseased oak trees and initially identified as B. stevensii was characterized on the basis of morphology and ITS nucleotide sequences. Morphology was compared with the type specimens of Physalospora mutila (= B. stevensii) and its anamorph, Diplodia mutila. It was concluded that the isolates from oak differed from B. stevensii in having larger ascospores and conidia as well as different spore shapes and represented an as yet undescribed species, which is described here as B. corticola. Moreover, ITS sequence data separated B. corticola from all other known species of Botryosphaeria. Amended descriptions of B. stevensii and its anamorph are provided to differentiate B. stevensii from B. corticola and to clarify some of the earlier taxonomic uncertainties.