Anatomical variations are very important to be identified when planning a paranasal sinus (PNS) surgery. Conventional radiology does not permit a detailed study of anatomical variations of the nose and paranasal sinuses; there is lack of studies in Saudi Arabia resident in this entity to Study Anatomical Variations of Para nasal sinus (PNS) using Multislice Computed Tomography (MSCT) in Rhinosinusitis. A cross-sectional hospital-based study of 392 patients, 272 males, 120 females, referred for CT scan of PNS was conducted from 2017 to 2019, this study was done in Riyadh Hospitals, Saudi Arabia, mostly from Consultant Radiologists Diagnostic Center selected all complaining from rhinosinusitis using Toshiba Alexion 16 slice. The images were evaluated for the presence of any anatomical variants in paranasal sinuses. The results of this study revealed that the absolute frequency of anatomical variations among 392 is 91.3% deviated nasal septum, concha bullosa seen in 50.77%, agger nasi cell found in 51.02%, Basal lamella pneumatization found in 5.36 %. The superior turbinates were pneumatized in 20.15%. The crista galli was pneumatized in 19.39%. frontal sinus was hyper pneumatized in 8.67% and non pneumatized in 4.85%, The middle turbinate found to be paradoxical in shape in 10.71 %. lamina papyracea dehiscence in 1.79%, inferior turbinate was pneumatized in 1.28%. The frontal air-cell was not present in our studied group. The supraorbital air-cell was present in 16.07%. The Onodi air-cell found to be present in 12.24%. The Haller air-cell found to be present in 30.10%. The sphenoid sinus is laterally pneumatized in 7.65%. The depth of cribriform plate (Keros classification) was in 0.51%. The infraorbital air-cell was present in 10.20%,nasal septum spur was presented in 29.34%, prominent ethmoidal bulla was presented in 29.85%, uncinate process was pneumatized in 12.76%,sphenoid sinus extension into posterior nasal septum is presented in 36.22%, posterior floor of sella turcica was pneumatized in 30.87%, the pterygoid process was pneumatized in 7.91%,anterior clinoid process was pneumatized in 10.97%, hard palate was pneumatized in 9.18% and lastly sphenoid septum change the direction in 8.16%. Anatomical variations of paranasal sinuses are best depicted on MDCT (multi detector computed tomography) scan of PNS. The deviated nasal septum is the commonest anatomical variation (93.11%) followed by agger nasi cell (51.02%).