Introduction: Functional endoscopic sinus surgery (FESS)has become most preferred  procedure in treatment of diseases of the nose and paranasal sinuses.The purpose of this study is todiscuss the incidence of skull base injury during surgery and radiologically analyse the depth of the olfactory fossa and the length of the lateral lamella in a CT PNS scan using the Keros classification, to determine the age and gender distribution, and to discuss its significance in surgical practice. Methodology: The is a retrospective study which was conducted among 200 patients above 10 years of age who visited ENT department in the past one year and had undergone CT PNS scan in radiology in VMKVMCH, Salem for sinusitis, headache, sinonasal polyposis and deviated nasal septum and those undergoing surgery. Scans of patients with previous history of surgery or trauma to nose and PNS and congenital anomalies of face were excluded. The results correlated with surgical relevance in FESS. Results: There were about 17% in Keros classification I, 78% Keros classification II and 6% Keros classification III.