The clinical and pathologic features of seven cases of a newly recognized form of chronic sinusitis are described. Most patients were young adults with a history of asthma, and all had chronic nasal polyps. Radiographically, there was opacification of multiple sinuses. Recurrent sinusitis was common, and several patients underwent numerous surgical drainage procedures. Histologically, a distinct mucinous material containing eosinophils, Charcot-Leyden crystals, and fungal hyphae was found in tissue resected from the sinuses. We believe that these findings constitute a distinct clinicopathologic entity that we term allergic Aspergillus sinusitis. This condition shares similar histopathologic features with allergic bronchopulmonary aspergillosis (ABPA) but affects the paranasal sinuses rather than the lung. Implications for therapy of this form of sinusitis and its possible relationship to allergic lung diseases are discussed.