Since accurate description on the pathophysiology of paranasal sinusitis was established, a detailed evaluation of anatomic and pathologic status of ostiomeatal unit of paranasal sinus has become important. Conventional plain sinus radiographic techniques failed to adequately detect minimal degrees of bony abnormalities of the PNS. However, computed tomographic techniques can clearly image abnormalities in these regions. We examined anatomical variations that may affect ostiomeatal unit with CT scan and evaluated relationship between anatomical variation of PNS and paranasal sinusitis. Of 56 normal cases, agger nasi cell was observed in 30 cases(53.6%), enlarged ethmoid bulla in 24 cases(42.9%), paradoxical middle turbinate in 2 cases(3.6%), and concha bullosa in 6 cases(10.7%). Of 162 paranasal sinusitis cases, agger nasi cell was observed in 114 cases(70.4%), enlarged bulla in 51 cases(37.7%), paradoxical middle turbinate in 28 cases(17.3%), and concha bullosa in 22 cases(13.6%). The paradoxical middle turbinate(p<0.01) and agger nasi cell(p<0.05) were more significantly detected in sinusitis group than normal group. These results suggest that paradoxical middle turbinate and agger nasi cel may be important anatomical factors which can predispose to the development of paranasal sinusitis.