Endoscopic sinus surgery (ESS) is widely utilized for the treatment of chronic paranasal sinusitis, We have compared preoperative PNS CT with endoscopic findings of 2450 cases who underwent ESS from August 1989 to August 1992 under diagnosis of chronic sinusitis. We have analyzed our cases by Babbels' five patterns of chronic sinusitis. The infundibular pattern (I) was identified in 319 cases (13%), ostiomeatal unit pattern (II) in 955 cases (39%), sphenoethmoidal recess pattern (III) in 270 cases (11%), sinonasal polyposis pattern (IV) in 906 cases (37%), and sporadic pattern (V) in 196 cases (8%). Mucosal edema, polyps and enlarged ethmoidal bulla were common causes of ostial obstruction in infundibular and ostiomeatal unit pattern.