The purpose of this study is to determine some important variations and dangerous areas carrying risks for major complications, in the routine CT examination. We also made specific measurements to evaluate the individual differences. This prospective study consisted of 111 patients (222 sides). Eighty patients underwent coronal, and the rest coronal and axial CT. The depth of lamina cribrosa, its distance to the inferior turbinate, and the distance of anterior ethmoidal artery (AEA) either to the orbital roof or inferior turbinate were measured. Variations of the upper attachment of uncinate process were encountered in 23%. AEA coursed freely within ethmoidal cells in 43%. Anterior clinoid aeration was seen in 14%, optic canal bulging into the sphenoid sinus in 13% and an extreme medial course of the carotid canal in 12% of the patients. The mean depth of lamina cribrosa was 5.9 mm, and its mean distance to the inferior turbinate was 25.7 mm. The mean distance of AEA to the orbital roof was 13.7 mm, and to the inferior turbinate 30.05 mm. Anterior clinoid aeration correlated well with the variations of carotid and optic canals, statistically (p < 0.01). A detailed CT study will provide important information on the areas carrying risks of complications and the size of the area to be worked on.