Objective: To determine the prevalence of sinonasal anatomic variations seen on paranasal sinus (PNS) CT scans of a sample of Filipino adults with chronic rhinosinusitis. Methods: Design: Cross-sectional study Setting: Tertiary Government Training Hospital Participants: The PNS CT scans of 51 Filipino patients with chronic rhinosinusitis with and without nasal polyposis diagnosed at our outpatien Department of Otorhinolaryngology-Head and Neck Surgery between October 2015 to December 2020 were reviewed for the presence of sinonasal anatomic variants. The prevalence of the identified variants was calculated. Results: The CT scans of 51 patients, 41 (80.4%) men and 10 (19.6%) women, were included. The median age was 48 years (Q25: 35, Q75: 56, IQR:21). The median Lund Mackay Score (LMS) was 15 (Q25: 12, Q75: 20, IQR:8). Majority (94%) had an LMS of ≥5. The most common anatomic variant in the study population was agger nasi (n=46/51, 90.2% present bilaterally) followed by uncinate process attachment to the lamina papyracea (n=90/102, 88.24%). The third to sixth most common findings were Keros type II classification (n=76/102, 74.51%), nasal septal deviation (n=35/51, 68.62%), optic nerve canal type 1 (n=67/102, 65.69%) and anterior ethmoid artery grade 1 (n=46/102, 45.1%), respectively. Less common variants were Onodi cell (n=13/51, 25.49% unilateral and n=10/51, 19.61% bilateral), Haller cell (n=8/51, 15.69% unilateral and n=1/51, 1.96% bilateral), supraorbital cell (n=4/51, 7.84% unilateral and n=4/51, 7.84% bilateral), middle turbinate concha bullosa (n=3/51, 5.88% unilateral and n=6/51, 11.76% bilateral), superior turbinate concha bullosa (n=2/51, 3.92% unilateral and n=1/51, 1.96% bilateral), pneumatized crista galli (n=2/51, 3.92%) and optic nerve dehiscence (n=1/51, 1.96% bilateral). Conclusion In the adult Filipino population with CRS sampled in this study, the six most common sinonasal anatomic variants were agger nasi, superior attachment of the uncinate process to the lamina papyracea, Keros type II classification, septal deviation, optic nerve canal type 1 and anterior ethmoid artery grade 1. Pre-operatively, the PNS CT scan of every patient must be meticulously evaluated for the sinonasal anatomic variants to avoid surgical complications.