Background: Nasal and sinus illnesses are diagnosed with computed tomography (CT) because CT scans effectively bone anatomy is depicted with air spaces, opacified sinuses, and detailed structural details. Objective: The significance of using multislice CT for the detection and characterization of sinus polyps and the relationship between the CT findings and those of functional endoscopic sinus surgery (FESS) have been studied. Patients and Methods: At Zagazig University's Radiodiagnosis Department, we conducted this study on 18 patients, 10 of which were females and eight were males, from a total of 33 individuals. To emphasize the role of multislice (CT) in diagnosis and characterization of sinonasal polypi during functional endoscopic sinus surgery, numerous CT parameters were used and correlated with operational findings. Results: There was a strong correlation calculated by Spearman correlation coefficient (r) for right-sided and left-sided surgeries of 0.76 and 0.87, respectively, for operative endoscopic and Lund-Mackay staging scores. Conclusion: Based on functional endoscopic sinus results, CT and diagnostic endoscopy may be the new standard of care in the diagnosis of sinonasal diseases.