Allergic reactions caused by fungi, may be present in the airways, skin, eyes, gastrointestinal tract, skin and to cause systemic reaction. Nasal symptoms react as allergic rhinitis. In a small group of patients the allergic fungal rhinosinusitis is present. It is important, because of the way of treatment, to differentiate the AFS from the other forms of chronic rhinosinusitis. The fungi may cause bronchial asthma, allergic bronchopulmonary aspergillosis and allergic alveolitis (hypersensitivity pneumonitis). Diagnostics of the allergic reactions caused by fungi includes routine allergological methods, mycologic culture and direct microscopic examination. The process of reaching the diagnosis of allergic fungal rhinosinusitis and allergic bronchopulmonary aspergillosis may require the CT and histopatologic examination. The treatment of fungal allergic reactions includes allergen avoidance, pharmacotherapy, antifungal treatment (id reactions) and surgical treatment (allergic fungal rhinosinusitis). The immunotherapy is a valuable, and accepted by the WHO therapy of the Cladosporium and Alternaria sensitive patients.