Nasal secretions, maxillary sinus aspirates and specimens of the maxillary sinus mucosa were collected in 44 patients aged between 25 and 60 affected by mono- or bilateral chronic maxillary sinusitis, in order to establish the best sampling technique for microbiological purposes, the most frequently involved bacteria and the physiopathological mechanism underlying chronic maxillary disease. The sinusal mucosa resulted to be the most reliable sample as it reduces contamination and microbial variability. Anaerobic bacteria were isolated in nasal swab (15.6%), in maxillary sinus aspirates (30.4%) and in maxillary sinus mucosa (36.4%) of maxillary sinusitis patients. In controls anaerobic bacteria were isolated only in one nasal swab (2.3%), while they could not be isolated in maxillary sinus aspirates and in maxillary sinus mucosa. The presence of anaerobic bacteria in chronic maxillary sinusitis patients and their absence in controls seem to confirm that anaerobic microorganisms represent the main pathogenetic agents of chronic maxillary sinusitis. The possible physiopathological mechanisms underlying chronic maxillary sinus disease are finally discussed.