Chronic paranasal sinus disease is one of the most common causes of application to physicians in pediatric and adult patients. In the surgical treatment of these diseases, endoscopic sinus surgery is an application that is often done to increase the quality of the patient's life. On account of this, the anatomic variations in skull basement must be well known to avoid possible major complications that may occur during the operation. Recent developments in paranasal sinus surgery also enhanced the need for examining exhaustively the anatomy of this region and existing pathology. Superiority of computed tomography (CT) has an unquestionable importance for the evaluation of anatomic structure and pathology compared with conventional radiographs. A likely anatomic knowledge is needed for a safe surgery. Before the surgery, determining the anatomic variations makes the operation safer and increases the prospects, so we can prevent complications that may occur during the surgery. In this study, CT coronal sections of 300 patients who were admitted to the Department of Ear Nose Throat of Medical Faculty of Cumhuriyet University Research and Training Hospital between the dates December 2008 and January 2011 with complaints of nasal flow and postnasal drip were studied. According to coronal section CT examinations, the patients were divided into 2 groups. Group 1, with 156 cases (64%), showed mucosal changes, and in 144 cases (36%), no mucosal changes were established (group 2). In comparison between the sexes, in groups 1 and 2 females, significant difference was determined for other parameters except the average height of the ethmoid roof. In the comparison between the sexes, in groups 1 and 2 males, significant difference was determined for all parameters. The difference between these 2 rates was statistically significant. Keros types 1 and 2 cases were compared with the control group, and there was no statistically significant difference. Notwithstanding, at the comparison of the Keros type 3 with the control group, there was a statistically significant difference for all the parameters (maximum orbital height, the length of the middle concha, and the nasal wall). It seems to be important for us to know the average length of the peripheral anatomic structures to avoid serious complications that may occur during the operation. Careful preoperative review of paranasal sinus CT scans in patients undergoing sinus surgery seems to be the most important to prevent severe intraoperative complications.