The Significance of ostia of the paranasal sinuses is that infection of one may easily spread to another. Anatomic abnormalities, irreversible inflammatory changes, or obstruction of ostiomeatal unit(OMU)-middle turbinate, uncinate process, bulla ethmoidalis, and infundibulum may lead to sinus obstruction and subsequent chronic or recurrent sinusitis. For these reasons, careful diagnostic examination of OMU is most important in surgical intervention of paranasal sinusitis. The middle turbinate is usually a thin plate of bone. However, anatomical abnormalities of middle turbinate-concha bullosa(pneumatized middle turbinate) and paradoxical middle turbinate (PMT)-may compress the uncinate process and occlude the infundibulum, and then they may induce anterior paranasal sinusitis. We examined anatomical variation of middle turbinate using paransal sinus computed tomography in paranasal sinusitis patients to evaluate the relationship between anatomical variation of middle turbinate and sinusitis. Among the 162 cases evaluated for sinus disease with paranasal sinus CT, 50(30.9%) cases had anatomic variation of middle turbinate. Of these cases, 28(17.3%) cases had PMT and 22(13.6%) cases had concha bullosa. Of anatomical variation of middle turbinate, only paradoxical middle turbinte was signficantly associated with high incidence of anterior ethmoidal sinusitis(p<0.05) and high incidence of sinonasal polyposis pattern(p<0.01). However, concha bullosa did not show any influence on the infection of paranasal sinuses. This study suggests that PMT may be one of the important anatomical factors among the several anatomical causes of paranasal sinusitis.