We isolated ascospores and conidia of fungi associated with leaf spots common in birch leaves, and prepared mycelial cultures from them. The taxonomic positions of the fungi were determined by analysing morphological characteristics with photomicroscopy. The relationship between the teleomorph and anamorph was tested using random amplified microsatellite fingerprints, in which the variation was not explained by the origin of isolates (e.g. ascospores or conidia). This suggested that the ascospores and conidia would have been produced by the same biological species. In pathogenicity tests birch leaves inoculated with mycelia derived from ascospores developed spots showing that the fungus could be the cause of the leaf spots. The anamorph was isolated from the developing spots. Based on these results and on review of the literature we concluded that the causative agent of the leaf spot disease of birch in Finland is Pyrenopeziza betulicola, the anamorph of which belongs to Cylindrosporium.