Aims: To study the anatomical variations of osteomeatal complex and the importance of preoperative computed tomography (CT) in patients with chronic sinusitis undergoing functional endoscopic sinus surgery. We studied the different variations and their frequency of occurrence. Materials and methods: A total of 100 patients undergoing endoscopic sinus surgery were studied by nasal endoscopy, CT scanning, and at the time of definitive surgery, variations were recorded. Results: The frequency of occurrence of sinonasal anatomical variations was septal deviation in 76%, agger nasi cells in 71%, concha bullosa in 61%, medialized uncinate process in 48%, prominent bulla ethmoidalis in 41%, paradoxical middle turbinate in 33%, accessory maxillary ostium in 28%, frontal cell in 22%, intumescentia septi nasi anterior in 21%, lateralized uncinate in 15%, pneumatized uncinate process in 4%, Haller cells in 12%, and Onodi cells in 8%. Conclusion: The high incidence of variations emphasizes the need for proper preoperative assessment for safe and effective endoscopic sinus surgery. © 2017 Elsevier B.V., All rights reserved.