Allergic fungal sinusitis is a noninvasive type of sinusitis. According to previ-ous reports from the USA, it accounts for approximately 6% to 8% of all cases of chronic sinusitis requiring surgical intervention. However, it has been rarely reported in Taiwan. According to the diagnostic criteria defined by the Mayo clinic, the diagnosis of allergic fungal sinusitis is made for all patients who demonstrate characteristic allergic mucin and one of the following: 1) fungal hyphae within the allergic mucin with no evidence of tissue invasion, or 2) positive results of cultures for fungi. The allergic mucin contains clumps or sheets of necrotic eosinophils against an amor-phous, pale eosinophilic or basophilic background. A 44-year-old female patient with multiple sinusitis and nasal polyopsis underwent bilateral func-tional endoscopic sinus surgery in November 1997. The pathological report of the sinus contents showed characteristic allergic mucin without fungal hyphae. A culture of the sinus contents revealed growth of Aspergillus fumi-gatus. This met the diagnostic criteria of allergic fungal sinusitis, and its details are discussed. The patient’s symptoms including nasal obstruction and post nasal dripping subsided after the operation. Thus FESS is an effect-tive surgical procedure to treat this kind of sinusitis.