In this study we report on the correlation between bacteriology and disease severity staging by computed tomography (CT) for chronic sinusitis. When patients with chronic sinusitis underwent functional endoscopic sinus surgery (FESS), swab specimens were taken from the ipsilateral middle meati and ethmoid sinuses under endoscope guidance. The severity of chronic sinusitis was evaluated by pre-operative CT scans. The CT scans were staged by the Lund and Mackay system. The scores for the frontal, anterior ethmoid and maxillary sinuses and for the ostiomeatal complex were added. The culture rates were correlated with the added scores. Between November 1998 and January 2003, 79 pairs of specimens were collected from 79 patients whose CT scans were done within a day before FESS. The culture rates of middle-meatus specimens were moderately correlated with the scores, but those of ethmoid sinus specimens were negatively correlated with the scores. If Staphylococcus epidermidis and corynebacteria were considered normal flora, the bacteriology of the middle meatus was highly correlated with the CT scores. This study shows that culture rates of middle-meatal specimens tended to increase with the severity of chronic sinusitis.