Aim. The objective of the present work was to study the species composition of the microflora isolated from the fungal ball of the paranasal sinuses. Materials and methods. We analyzed the results of the bacteriological investigation of the contents of the paranasal sinuses in 148 patients who had undergone an endonasal endoscopic surgical intervention for the treatment of chronic rhinosinusitis. Multi-spiral computer tomography located fungal balls in the maxillary sinuses of 113 patients, in the sphenoidal sinuses of 25 patients, in the ethmoidal sinuses of 7 patients, and in the frontal sinuses of 3 patients. Results. Inoculation of the sinus contents into selective media and their cultivation under two temperature conditions (28 and 37 °С) revealed the growth of filamentous fungi isolated from 26 patients. Aspergillus spp prevailed among the identified fungi (they were found in 14 out of 26 patients). The absence of the microbial growth in the cases of visual discovery of the fungi by microscopic and histopathological examination can be possibly attributed to the staged development of the fungal balls and the death of the fungi at the late life stages.