Mycotic eosinophil rhinosinusitis causes diagnostic and in particular etiopathogenetic difficulties. Although it is associated with classical manifestations of allergy, the latter can be detected only in a minor proportion of patients. There are also doubts on the action of fungi as the primary noxious agent. A typical sign is a mucous exudate containing mycotic hyphae and disintegrating eosinophils originating from the mucosa, Charcot-Layden’s crystals and large basic proteins. The tissues are not infiltrated by fungi. The troublesome disease is clinically manifested similarly as the ASA syndrome. In treatment dominate palliative endoscopic rhinosinosurgery and corticoids. The disease belongs into the group of non-allergic rhinosinusitis with the eosinophil syndrome (NARES); it has nothing in common with the caseous mycotic sinusitis characterized above all by the formation of mycetomas, nor with lethal invasive forms of fungal rhinosinusitis.

        Key words: rhinosinusitis, fungi, eosinophilia.