Although first described in 1983, allergic Aspergillus sinusitis (AAS) has yet to gain wide recognition among otolaryngologists and pathologists. We have treated three patients with a history of asthma, nasal polyposis, and recurrent pansinusitis who fit the description of allergic Aspergillus sinusitis. Histopathologically, mucinous material with abundant eosinophils and Charcot-Leyden crystals ("allergic mucin") is interspersed with fungal hyphae. Immunologic characteristics include serum total immunoglobulin E (IgE) elevation, increased RAST classes, and cutaneous reactivity to molds. A retrospective analysis of the histopathology of 82 patients with chronic sinusitis was also undertaken. Eleven additional patients with classic allergic mucin were identified, but were found to be without evidence of fungal elements. The clinical features of all 14 patients are reviewed revealing the spectrum of disease. The difficulties of diagnosis and a therapeutic protocol which includes wide local debridement and postoperative use of systemic steroids are discussed.