Background: Chronic sinusitis (CS) is a disease that affects a significant percentage of the population and causes considerable long term morbidity. This study evaluates different microorganisms causing CS and their microbial RESISTANCE to antibiotics.Methods: Eighty-eight patients with CS requiring a sinus endoscopic surgical procedure were evaluated. At the time of sinus endoscopy, samples were obtained and cultured for aerobes, anaerobes and fungus infections. Demographic data, disease symptoms and signs, culture results and antibiograms were recorded in checklists.Findings: A total of 88 patients (55.3% males and 44.7% females) with a mean age of 38±16 years and 88 cultures were studied. Coagulase-negative staphylococci were the most common pathogen (29.5%), followed by staphylococcus aureus (19.2%), klebsiella (14.1%), E-coli (12.8%), enterobacter (6.4%), and streptococcus hemolytic group A and non-A, Citrobacter, Pseudomonas and muconnycosis. The most common antibiotic RESISTANCE was to ampicillin and penicillin-G and the most common antibiotic sensitivity was to ciprofloxacin and cephalosporins.Conclusion: This study demonstrates that aerobic pathogens rather than anaerobic bacteria or fungi are more common pathogens in CS. Presence of a chronic disease, geographical and socioeconomic factors, as well as a wide variety of invasive organisms are involved in the etiology of sinusitis. Inappropriate use of antibiotics - particularly penicillins - has caused the present DRUG RESISTANCE in sinusitis.