Several elm-infesting bark beetles belonging to the genus Scolytus (Coleoptera: Scolytinae) are vectors of Ophiostoma spp., most notably the Dutch elm disease fungi. A related bark beetle species, Scolytus ratzeburgi, is known to infest birch in various parts of Europe, but it is unknown whether fungi are associated with this beetle. The aim of this study was to identify several fungal species isolated from S. ratzeburgi. Beetles and their galleries were collected from Betula pendula at three different sites in the boreal forests of the Karelia region, on both the Finnish and Russian sides of the border. Three ophiostomatoid fungi were isolated from the beetles and their galleries. One Penicillium and one Bionectria species were isolated only from the Finnish material and, based on DNA sequences, were identified as P. brevicompactum and a species close to the anamorph of B. zelandianovae. Two Ophiostoma species present in low numbers included O. quercus and a species closely related to O. catonianum. Only one Ophiostoma species was isolated consistently from all the galleries and beetles considered in the study. Comparison of DNA sequences and morphological characterization showed that this fungus represents an undescribed taxon, described here as O. karelicum sp. nov.