<p class="abstract"><strong>Background:</strong> Variations in sinonasal anatomy of adults<strong> </strong>are common and vary among different populations. Their role in development of pathological conditions such as sinusitis, epistaxis, etc is debated. Having clear picture of sinonasal anatomy of a person is essential in avoidance of complications during surgery. This study was done<strong> </strong>to<strong> </strong>analyze<strong> </strong>sinonasal anatomy in adults from Karaikal region having chronic sinusitis by nasal endoscopy and CT scan imaging.</p><p class="abstract"><strong>Methods:</strong> A total of 50 patients undergoing endoscopic sinus surgery were studied by preoperative nasal endoscopy, CT scanning and endoscopy at the time of definitive surgery and variations recorded and analyzed. </p><p class="abstract"><strong>Results:</strong> The incidence of the sinonasal anatomical variations in CT scan study were – discharge in the frontal sinus (100%), agger nasi cells (96%), deviated nasal septum (70%), anterior ethmoidal cells (86%), posterior ethmoidal cells (58%), sinus lateralis (52%), frontal cells (50%), discharge in sphenoid sinus (50%), pneumatised superior turbinate (46%), INSA (34%), prominent bulla ethmoidalis (30%), supra orbital cells (26%), pneumatised septum(16%), medialised uncinate process (16%), paradoxical middle turbinate (16%), Haller cells (14%), supreme turbinate (14%), pneumatised inferior turbinate (12%), frontal recess obliteration (12%), absent pneumatisation of frontal sinus (12%), pneumatised middle turbinate (10%), Onodi cells (6%), pneumatised uncinate process (2%), maxillary sinus septation (2%).</p><p><strong>Conclusions:</strong> The high incidence of variations emphasises the need for proper preoperative assessment for safe and effective endoscopic sinus surgery. </p>