Fungus ball (FB) of the paranasal sinuses has a distinctive clinicopathological presentation. The disease occurs more frequently in elderly patients and has a female preponderance. Classically, it involves only one paranasal sinus in more than 90% of the cases, most commonly the maxillary sinus. Imaging characteristics (calcifications and / or erosion of the inner wall of the sinus visible on CT) and histopathological ones (luminal aggregation of fungal hyphae) confirm the diagnosis. Allergic fungal rhinosinusitis (AFRS) usually occurs in younger, immunocompetent patients, with a history of atopy, including allergic rhinitis and / or asthma, or a long clinical picture of chronic rhinosinusitis (CRS), refractory to antibiotic treatment. Nasal polyps (NP) are present in almost all patients, while extra-sinusal complications are described only in some of them. Usually, there is involvement of several sinuses, as well as bilateral damage. The definitive diagnosis is confirmed only by examining surgical specimens - the characteristic appearance of eosinophilic mucin is the most reliable indicator of AFRS.