In this study we report on the correlation between the bacteriology of the middle meatusand ethmoid sinus in chronic sinusitis. When patients with chronic sinusitis underwent functional endoscopicsinus surgery (FESS), swab specimens were taken from the middle meati before surgery. After removing the ethmoid bullae, swab specimens were taken from the ethmoid sinuses. Between November 1998 and February 2001, 186 pairs of middle meatal and ethmoid sinus specimens were collected from 186 patients. No bacteria were cultured from either specimen in 32 patients. The same bacteria were cultured from both specimens in another 60 patients. The culture results differed between the middle meatal and ethmoid sinus specimens in the remaining 94 patients. There was a significant difference between culture rates of 63.4 per cent for middle meatal specimens and 76.3 per cent for the ethmoid sinus specimens. In analysing bacterial species, significantly more aerobic Gram negative bacteria were cultured from the ethmoid sinus specimens than from the middle meatalspecimens. This study shows that the bacteriology of the middle meatus was different from that of the ethmoid sinus. Therefore, the bacteriological findings in the middle meati may not reflect the real bacteriology in chronic sinusitis.