Background: Pew eases of allergic fungal sinusitis have been systematically evaluated to conclusively confirm working clinical, histopathologic, and serologic diagnostic criteria. Objectives: The objective of this study was to describe 67 consecutive cases of allergic fungal sinusitis, the largest number of cases Set published. Methods: Cases from 1 practice over 8 years were evaluated with a consistent protocol, including skin testing, serum chemistries and serologies, and surgical specimen analysis. Results: All patients were atopic (100%) and had nasal polyposis (100%). They tended to be young (33.3 +/- 13.1 years, mean +/- SEM), immunocompetent (92%; remaining 8% with low quantitative immunoglobulin but normal function), have slight female preponderance (58%), have a history of hypertrophic rhinosinusitis (100%), report nasal cast production (75%), and have developed their disease in the southwestern United States. Bipolaris spicifera was the most prevalent fungus involved (67%). Total serum IgE (mean 668 IU/mL) and fungal-specific Ige were generally elevated, whereas fungal-specific precipitins and specific IgE were generally negative despite positive fungal-specific immediate hypersensitivity skin tests. Conclusions: Patients with allergic fungal sinusitis tend to have elevated total serum IgE and fungal-specific IgG at diagnosis but not fungal-specific IgE or precipitins, Histopathologic criteria for allergic fungal sinusitis diagnosis are discussed. The southwestern United States appears to be a "hot spot" for the disease, particularly caused by B spicifera.