Chronic sinusitis and its complications are often caused by fungi. In Europe and North America Aspergillus species are the most frequent contaminants of the sinuses, with relatively few cases of mycoses by Mucor, Candida, Penicillium and Cladosporium reported in literature. Though mainly saprophytic fungi, Aspergillus and especially Mucor may cause severe, potentially lethal complications. Consequently, therapy should include complete removal of the mycotic masses and prevent reinfection. Due to anatomical and physiological conditions, frontal and maxillary sinus infection derives from a chronically infected ethmoid in almost all of the cases. Endoscopical operation of the diseased ethmoid is hence an importand factor in our treatment schedule: Stenotic and/or chronically infected areas of the anterior and middle ethmoid are localised by X-ray tomography and/or CT. Then these areas are first inspected with the endoscope and then endoscopically operated, creating a large ostium by opening the infundibulum into the sinus. If it is impossible to remove all mycotic masses through this new window, an anterior approach is made in a third stage via the fossa canina. The fungus is removed, leaving the sinus mucosa untouched. There is no need for a window to the inferior nasal meatus. For follow-up treatment instillations of antimycotic creams are applied (Imidazole and Naftifine). The endoscopic operative technique is described in detail and its advantages and possible difficulties are discussed. 48 patients were studied and followed up for this paper.