Until several years ago, no criteria for diagnosis or consensus on the classification of fungal sinusitis existed. Many reports were grouped under the heading of "aspergillus sinusitis," regardless of invasiveness; thus, published information on the diagnosis, natural history, and treatment of fungal sinusitis was of limited value. Diagnostic criteria and clinical descriptions for allergic fungal sinusitis, sinus mycetoma, and invasive fungal sinusitis have now been published. These criteria, a new classification system, and the clinical approach to patients with fungal sinusitis are reviewed in this article. Although fungal sinusitis is not a rare disease, much remains to be learned about its optimal clinical management.