In the last fifty years, only 22 medical cases involving the basidiomycetous fungus Schizophyllum commune were reported. In a period of three years we have examined 270 patients suffering from chronic rhinosinusitis as well as from mycoses (fungus balls) within the paranasal sinuses. Either nasal mucus or fungal concrement from the sinuses were cultured and the resulting cultures identified microscopically. In cases, where a reliable identification of the fungi was not possible, DNA was extracted for molecular examination. The internal transcribed spacer (ITS) region of the ribosomal gene-cluster was amplified with fungus specific primers and sequenced thereafter. In addition, DNA of all fungi growing with sterile white mycelium was amplified with the primer pair scom1/scom2r, which is specific for S. commune. Altogether, within a three years period S. commune was isolated in twelve patients. It can be assumed, that with the presented methods S. commune will be found much more frequently in patients suffering from diseases of the nasal sinuses.