Aim of the study. Qualitative and quantitative analysis of cases of paranasal sinus and nasal cavity fungus balls in patients of the Otolaryngology Department of the Military Institute of Medicine in Warsaw between 2000 and 2017. Materials and methods. The study group was composed of 101 patients treated for fungus balls in the years 2000–2017. During that period 3 of the patients were treated twice, thus a total of 104 operative treatments were analyzed. Patient records, location and symmetry of lesion, type of treatment and special accompanying factors were analyzed retrospectively. Results. In 80 cases fungus balls affected a single maxillary sinus, in 10 – the sphenoid sinus, in 3 – the anterior ethmoidal sinus and in one case – the nasal cavity. Isolated fungus balls did not affect the posterior ethmoidal sinus and the frontal sinus. Concomitance of fungus balls in several paranasal sinuses, in the maxillary sinus and the nasal cavity and cases of bilateral occurrence were found. All patients underwent surgical treatment, of which 78.8% was FESS, without an anti‑fungal drug cover. In 102 cases, the etiological factor of the fungus balls were fungi of the genus Aspergillus and in two other cases – genus Candida. Conclusions. Fungus balls, most often caused by members of the genus Aspergillus, occur mostly unilaterally in the maxillary sinus. The FESS is an effective and safe method of treatment.