Background: Surgical landmarks for defining the level of the skull base during endoscopic sinus and skull base surgery (ESBS), e.g., the middle turbinate, may be distorted by tumor or previous surgery. The orbital floor is a valid fixed anatomic landmark for the white population, but it is not known if its use is useful for an Asian population. Objectives: To define fixed anatomic landmarks for ESBS in an Asian population and to compare the level of the skull base and its relation with anatomic landmarks between Asian and white populations. Methods: Computed tomographies performed on paranasal sinuses of Thai patients were retrospectively assessed. The distance between the nasal floor to four structures, the orbital floor, sphenoid planum, cribriform, and ethmoid roof, were measured. The level of skull base related to the orbital floor of an Asian population was compared with data of a white population from a previously published study. Results: A total of 150 Thai patients (300 paranasal sinus systems) were assessed and compared with 150 white patients. The orbital floor was always below the skull base (600 sides [100%]). When compared with white patients, the Asian patients had significantly higher mean (standard deviation [SD]) values: orbital floor (35.2 ± 3.4 mm versus 33.9 ± 3.0 mm; p < 0.001), ethmoid roof (49.3 ± 3.8 mm versus 48.4 ± 4.5 mm; p = 0.01), cribriform (46.4 ± 3.6 mm versus 44.0 ± 3.7 mm; p < 0.001), and sphenoid roof (45.7 ± 3.7 mm versus 44.9 ± 3.7 mm; p = 0.01). The Asian population had a mean (SD) longer distance from the orbital floor to the cribiform (11.2 ± 2.5 mm versus 10.1 ± 2.7 mm; p < 0.001), a shorter distance to the sphenoid roof (10.5 ± 3.3 mm versus 11.0 ± 2.9 mm; p = 0.03), and a similar distance to the ethmoid roof (14.1 ± 3.1 mm versus 14.5 ± 3.5 mm; p = 0.09). Conclusion: Although a statistical difference exists between racial groups, clinically, the orbital floor is a useful fixed anatomic landmark for ESBS for both Asian and white populations.