Endoscopic sinus surgery as a surgical technique for nasal and paranasal sinus surgery has become very popular. In contrast to traditional operations, limitation of the surgeon's vision through a telescope in endoscopic surgery can lead to a loss of perspective of the patient's entire head. And anatomical variations in each patient increases the risk of inadvertant injury to the neighboring structures. In order to decrease the risks of endoscopic sinus surgery, the authors have calibrated distances and angles between the anterior nasal spine, mid-fovea ethmoidalis, sphenoethmoid junction, anterior face of sphenoid, and posterior wall of the sphenoid using PNS CT.