Recently, as the endoscopic technique has been adopted as a standard method of sinus surgery, preoperative radiologic findings and the nasal endoscopy have become necessary for preoperative information about anatomical variations and the degree of sinus pathology. For the radiologic study, we designed a PNS screening CT scan which is a coronal cut of PNS CT scan. The PNS screening CT scans are much more accurate than PNS plain X-rays and less expensive and time saving in comparison with the PNS CT scans. We carried out PNS screening CT scans and PNS plain X-rays on the same day in 30 patients, and the results are as follows. 1) The findings of PNS plain X-rays and PNS screening CT scans were not always compatible, with maxillary sinus most reliable. 2) We had more accurate information such as the mucosal conditions of each sinus, the fine structures in the middle meatus, and the anatomical variations of lamina papyracea and skull base from the PNS screening CT scans than from PNS plain X-rays. We could, therefore, minimize the extent of operative procedures and decrease the possibility of complications during the operation. 3) On the basis of the PNS screening CT scan, we propose a staging system according to the degree of sinus involvement. The staging system of sinusitis may serve as a guide in adopting a surgical technique and in assessing prognosis.