Chronic sinusitis is one of the most common diseases treated in outpatient centres. In this prospective study, 49 patients with the diagnosis of chronic maxillary sinusitis were evaluated microbiologically by using sinus swab, irrigation fluid and sinus mucosal tissue specimens obtained during endoscopic sinus surgery. There was no bacterial growth in seven cases. In the remaining 42 cases a total of 89 bacteria were isolated, 28 of them being classical pathogens and 61 being non-classical pathogens. Among the classical pathogens Staphylococcus aureus was the most common one. The correlation between the isolates obtained from maxillary sinus and isolates obtained from throat, nose and nasopharynx did not have a predictive value. Since the overall rate of classical pathogen isolation from patients with chronic sinusitis was not significantly high, the possible role of factors other than bacterial growth should be identified in the pathogenesis of chronic sinusitis.