Radiologic evaluation is indispensable for diagnosis of chronic sinusitis. Ostiomeatal unit computed tomography(OMU CT) was known to be more accurate than a conventional X-ray. However, many clinicians prefer conventional X-ray as screening test for low cost, small radiation dose and easy perfomance. We compared OMU CT with conventional X-ray views in 306 pa tients(612 sides) who were suspected of having chronic sinusitis. Coronal CT was taken after conventional X-ray examination, and intervals between the two examinations were 0 to 4 days. Correspondence rate of OMU CT findings with conventional X-ray ones was 72.1% in the maxillary sinuses of adult group, 60.0% in the ethmoid sinuses of the same group, 47.4% in the maxillary sinuses of pediatric group, and 38.8% in the ethmoid sinuses of the same group. If all OMU CT finding had been accurate, the rate of false negative with convention X-ray views was 9.7% in maxillary sinuses of adult group, and 15.1% I ethmoid sinuses of same group, 16.4% in maxillary sinuses of pediatric group, and 15.6% in ethmoid sinuses of same group. While, rate of false positive was 3.4% in maxillary sinuses of adult group, and 0.6% in ethmoid sinuses of same group, 10.3% in maxillary sinuses of pediatric group, and 4.3% in ethmoid sinuses of same group. Our result indicates that if conventional X-ray finding are doubtful in dianosis of sinus pathology or surgical intervention is planned, it is necessary to recommend CT.