To investigate the impact of the presence and the severity of the nasal septal deviation (NSD) on the paranasal pneumatization.Initially, the deviated and contralateral sides was compared to evaluate the impact of the presence of NSD on pneumatization. Then, NSD classification groups were categorized according to the severity of deviation degree; 1: mild (<9°), 2: moderate (9°-15°), and 3: severe (>15°). Pneumatization of all paranasal sinuses, osteomeatal complex (OMC), frontoethmoid recess (FER) and variant structures were compared according to the NSD classification groups separately both for the deviated and the contralateral sides.Although there was no statistically significant difference in pneumatization of the paranasal sinuses between the deviated and contralateral sides, a significant difference was observed in OMC and FER diameters. In the deviated side, there was statistically significant difference in ethmoid sinus volume, in FER and OMC diameters between NSD classification groups. In the contralateral side, FER and OMC diameters were found to be significantly different between group 1 and group 2 and between group 1 and group 3, respectively (P = 0.04 and 0.06, respectively). Both the presence and severity of the NSD did not statistically significant influence the pneumatization of variant structures, air cells and vital structures.The severity of NSD effects the ethmoid sinus volume. The relationship of FER and OMC with NSD is evident, however this may not always be in a proportional pattern. The paranasal pneumatization did not affect Keros type, bone integrity of carotid canal and optic canal.