Chronic paranasal sinusitis is a disease that afflicts a significant percentage of the population and causes considerable long-term morbidity. With the common use of multiple courses of broad-spectrum oral antibiotics to treat this condition, there is a possibility of an alteration in the pathogens that promote a persistence of chronic sinusitis. One hundred seventy-four consecutive patients with a diagnosis of chronic maxillary sinusitis requiring an endoscopic surgical procedure were prospectively evaluated. At the time of surgery, cultures of mucopus in the maxillary sinus were aseptically obtained endoscopically and cultured for aerobes, anaerobes, and fungus. Two hundred seventeen isolates from 174 patients were obtained. Coagulase-negative staphylococci were the most common isolates (36%), followed by Staphylococcus aureus (25%), Streptococcus viridans (8.3%), Corynebacterium (4.6%), and anaerobes (6.4%). Although coagulase-negative Staphylococcus is not considered a pathogen, of the 24 isolates that had sensitivity testing performed, 13 demonstrated resistance to multiple antibiotics, including cephalothin, erythromycin, oxacillin, sulfonamides, and clindamycin. This study demonstrates that aerobic rather than anaerobic bacteria are the more common pathogens in chronic sinusitis. In addition, coagulase-negative Staphylococcus may be a pathogen in the disease process, and sensitivities should be obtained of this isolate for evaluation and possible treatment.