As the endoscopic sinus surgery continues to gain popularity and support, a clear and accurate understanding of the anatomy of ostiomeatal unit becomes essential. The lateral lamella of the lamina cribrosa constitutes the lateral border of the olfactory fossa with the lamina cribrosa providing its floor. Lateral lamella presents the least resistance to probing instrument, being only 1/10 as strong as the roof of the ethmoid sinus. It was reported that the lateral lamella has a mean thickness of 0.2mm. A detailed analysis of coronal plane CT scans of the paranasal sinuses obtained in 120 consecutively imaged cases was conducted. Special attention was directed toward measuring the length between cribriform plate and ethmoid roof(lateral lamella of the lamina cribrosa). The results were as follows : 1) The length of lateral lamella was 3.1±1.4m(3.4±1.6mm in male and 2.7±0.9mm in female). 2) The angle of lateral lamella was 62.9±10.7°(62.3±11.1° in male and 64.1±9.7° in female). 3) The depth of lateral lamella was 1.8±0.5mm(1.9±0.9mm in male and 1.7±0.7mm in female). 4) The width of cribriform plate was 3.8±0.9mm(3.9±0.9mm in male and 3.6±0.7mm in female). 5) In comparison right side with left side, the depth of lateral lamella was longer in left side than right side. 6) In comparison sinusitis group with non-sinusitis group, the length of lateral lamella was longer in non-sinusitis group than sinusitis group.