Chronic rhinosinusitis (CRS) is a common inflammatory condition of nasal and paranasal sinus mucosa. Although pathogenic bacteria were postulated as main etiological factor responsible for most cases of CRS, the involvement of molds was recently proved in some cases. The aim of the study was to conduct mycological analysis of material obtained from patients operated on due to chronic sinusitis. The study included 107 patients, 45 women and 62 men. During the surgery, a fragment of mucosa from the region of the ethmoid bulla was obtained as microbiological characteristics of this material closely resemble those of sinus mucosa. In addition, maxillary sinus lavage was obtained. The control group comprised patients without chronic sinusitis. The dithiothreitol solution method was used for the lavage examination. The tissue material (mucosal fragment from the region of the ethmoid bulla) was incubated in 2% liquid Sabouraud medium for 24 h. The material was inoculated onto culture media. The presence of molds was detected in 67% of examined samples. Overall, 41 species belonging to 12 genera were isolated. The most frequently detected genera included Penicillium spp. (46%) and Aspergillus spp. (16%). In addition, Cladosporium spp. (11%), Fusarium spp. (7%), Acremonium spp. (4%), Eurotium spp. (4%), Alternaria spp. (2%), Chaetomium spp. (1%), Geotrichum spp. (1%), Verticillium spp. (1%), Rhizopus spp. (1%), and some unidentified colonies (5%) were isolated. Penicillium crustosum, Penicillium citrinum, Aspergillus niger, Cladosporium cladosporioides, and Fusarium verticillioides were the most prevalent species.