Allergic fungal sinusitis (AFS) is a noninvasive disease first described as a distinctive clinical and histopathologic entity more than 10 years ago. The typical patient is immunocompetent, atopic, has chronic sinusitis refractory to medical therapy, and 100% of those we have diagnosed have nasal polyps. Because of the histopathologic similarity to mucoid impaction of the bronchi seen in allergic bronchopulmonary aspergillosis, Aspergillus species were initially suspected as the causative agent. Subsequent reports include a number of non-Aspergillus-related cases. Both we and others have found a 7% incidence of AFS among chronic sinusitis patients requiring surgery. Relapse after surgical debridement and aeration is common and often responds to systemic corticosteroids. The diagnosis of AFS should be considered in all atopic patients with nasal polyps and chronic sinusitis. The clinical and histopathologic features of this disorder are reviewed.