BACKGROUND Many host factors even in immunocompetent patients may have an influence on development of a fungal diseases within the paranasal sinuses. Fungal sinusitis can occur in an acute form or more often to a chronic type of the disease. These mainly relatively asymptomatic chronic forms and further divided into a chronic noninvasive, chronic allergic, and chronic invasive disease. Endonasal microsurgery has significantly changed the management of chronic fungal sinusitis and allows adequate removal of pathologic tissue even in advanced situations. The aim of this study was to analyze the efficacy of endonasal surgery in chronic fungal sinusitis. METHODS In a retrospective study we assessed a group of 40 patients who had endonasal surgery for chronic fungal sinusitis. Patient records, CT and MRI scans, microbiology and histology as well as the postoperative clinical follow-up including endoscopic photo documentation were evaluated over a period of 5 years. All patients underwent endonasal surgery using endoscopic techniques. The microscopic was of additional help in a few cases with extended disease and multiple dehiscences of the skull base. RESULTS Twenty-four patients had a chronic noninvasive of fungal sinusitis and 16 patients had a chronic invasive form. All these patients underwent endonasal surgery without external incision. The fungal disease was erradicated in 39 cases, and revision surgery was required in only one case in which involvement of the contralateral side was not initially detected. in two cases scar tissue in the middle meatus was later excised but without evidence of residual fungal disease. Only in 6 cases was antifungal chemotherapy required, where the disease had spread into surrounding tissue or the patient had severe symptoms. CONCLUSIONS Endonasal microsurgical techniques are today the appropriate approach for managing chronic fungal sinus disease even in severe cases with radiologic evidence of expansion or invasion of surrounding tissue. Additional antifungal chemotherapy is only rarely indicated, specifically when the fungal disease invades surrounding tissue.