목적: The identification of anatomic landmarks in endoscopic sinus surgery (ESS) is essential. The medial maxillary sinus roof(MMSR) is easily identifiable during ESS and has been regarded as a reliable anatomic reference point for ESS. This study was performed to evaluate the relationship between MMSR and the sphenoid and posterior ethmoid sinus in Korean. 방법:One hundred forty consecutive ostiomeatal computed tomographic (OMUCT) scans from patients with various rhinologic symptoms were reviewed, giving a total of 280 sides for analysis. Using the nasal floor as a reference point, the vertical distance to the MMSR, natural sphenoid ostium, anterior sphenoid roof and floor and posterior ethmoid skull base were measured. In addition, the maxillary sinus to posterior ethmoid height ratio was calculated for each patient. 결과:Relative to the medial maxillary sinus roof, the mean vertical distance to the natural sphenoid ostium, sphenoid roof, and sphenoid floor was -0.952.87 mm, 11.682.83 mm, and 6.542.92 mm, respectively. The mean vertical height of the posterior ethmoid skull base was 14.932.88 mm. The mean maxillary sinus to posterior ethmoid height ratio was 2.411. 결론:The MMSR can be used as a reliable landmark to localize the natural sphenoid ostium and to enable a safe entry into the posterior ethmoid.