Background: endoscopic sinus surgery (ESS) is a common operation for the management of sinonasal pathologies, the surgeons dealing with endoscopic sinus surgery should understand the crucial complex anatomy of the anterior cranial base to avoid the intracranial violation during ESS. Objective: the aim of this work is to investigate the relationship between degree of septal deviation angle and the dimensions of cribriform plate and ethmoid roof by radiological paranasal CT evaluation. Patients and methods: forty patients, 20 females and 20 males, were selectively collected according to inclusion and exclusion criteria from the out-patient E.N.T clinics of El-Hussein and Bab-El-She'reya Hospitals from November 2017 to January 2019 with their age ranged from 18 – 60 years old. Results: the severity of deviation didn't have impact on the dimensions of the ethmoid roof and cribriform plate in terms of depth and width except right ethmoid roof width (direct proportion) and the left cribriform width (inverse proportion). There was a significant direct relationship between ipsilateral and contralateral ER width and between ipsilateral and contralateral ER depth. This study showed no significant relation between ipsilateral and contralateral CP width. High rate of asymmetry between CP and ethmoid roof in our study (100 %) was noted. Conclusion: in cases of deviated nasal septum, this study suggests that the increase in the severity of septum deviation rises the possibility of the increasing right ethmoid roof width and of decreasing the left cribriform width and this possibility should be taken into consideration to avoid iatrogenic injury during ESS.