Introduction: Olfactory loss is most commonly associated with the development of chronic sinusitis (CS) and as many as 28-84% of patients with CS have some degree of olfactory loss. According to EPOS guidelines, olfactory loss is one of the cardinal symptoms in diagnosing CS, with a significant correlation between olfactory loss and the degree of opacification of paranasal sinuses. In isolated and localized CS, olfactory loss is less pronounced, so it is easy to overlook the correct diagnosis. Isolated CS, particularly odontogenic maxillary sinusitis (OMS), may remain unrecognized for years and olfactory loss does not have the same intensity, frequency and significance as in other sinusitis. Odontogenic sinusitis accounts for 10-40% of all maxillary sinusitis. They are thought to occur due to a previous odontogenic infection, dentoalveolar or periodontal surgery or resistance to conventional therapy. Although much is known today about the correlation between a sinus CT scan, the endoscopic finding and CS properties, there is very little information on the correlation between olfactory test results and CS. Aims: The purpose of this study was to determine the role of olfactory loss in the diagnosis of isolated OMS and to assess the correlation of olfactory loss with volumetric sinus values that most accurately reflect mucosal thickening. Therefore, we compared the results of clinical olfactory tests with volumetric values of sinus mucosa using multislice computed tomography (MSCT), i.e. with the values of the mucosa according to the Lund-Mackay scoring in two isolated sinusitis: sphenoid sinusitis (SS) and odontogenic maxillary sinusitis (OMS). The sphenoid sinuses are located in the immediate vicinity of the olfactory region of the nose, while the maxillary sinuses are furthest from the specified region. The severity of the patient's disease was evaluated using the SNOT 22 test. Patients and methods: The study included 50 patients with OMS with a normal finding of sphenoid sinuses and the olfactory region and 50 patients with SS with or without edema of the olfactory region with normal findings of maxillary sinuses. To assess the severity of clinical symptoms, patients completed the SNOT 22 test which combines the symptoms, emotional and social aspects of rhinosinusitis. CT axial scans and their reconstruction allowed for a threedimensional (3D) volumetric analysis of the mucosa thickness of inflamed maxillary and sphenoid sinuses to be done. CT scans enabled the assessment of inflamed sinus mucosa or sinus fluid accumulation by the semiquantitative method using Lund-Mackay scoring on the same side as the examined maxillary or sphenoid sinusitis. The CT also assessed the degree of obstruction of the olfactory region on the same side as the examined sinusitis by using the scale of lesions of the olfactory region (OC scale). The olfactory examination was performed by clinical olfactory tests consisting of a threshold test, a discrimination test, and an identification test. The sum of the results of all three mentioned tests yields a TDI score, i.e. total olfactory test result. MedCalc Statistical Software version 19.3.1 (MedCalc Software Ltd, Ostend, Belgium; https://www.medcalc.org; 2020) was used in the data analysis. Results: The results showed that compared to maxillary sinusitis, sphenoid sinusitis have a statistically significantly higher incidence of hyposmia and anosmia (P <0.001). Olfactory tests are retained mainly in the range of normosmia in OMS, regardless of the degree of mucosal thickening and the severity of the clinical symptoms of sinusitis. The TDI and the percentage of the obliteration volume demonstrate that the correlation in SS (rho = -0.678, P <0.001) is more than twice as large than in OMS (rho = -0.307, P = 0.030) which leads to the conclusion that in regards to OMS, the sinus obliteration volume has half the effect on olfactory function in comparison to SS. By comparing the correlations between TDI and the obliteration volume percentage (rho = -0.678, P <0.001 for SS and rho = -0.307, P = 0.030 for OMS) and TDI and LM scoring for both sinusitis (rho = 0.691, P <0.001 for SS and rho = -0.464, P <0.001 for OMS), it is concluded that in the assessment of olfactory disorders, volumetric analysis is as valuable as L-M scoring. Conclusion: Olfactory tests do not have equal significance in all CS localizations. In the case of OMS, olfactory loss is significantly less common than in sphenoid sinusitis and cannot be defined as a cardinal symptom, which is why this type of sinusitis often goes unrecognized. Therefore, olfactory loss in OMS cannot be one of the main criteria of EPOS guidelines in diagnosing chronic sinusitis. In OMS, the volume of sinus obliteration has half the effect on olfactory function in comparison to SS. In the case of SS, the olfactory function is highlydependent on the mucosal thickening of all paranasal cavities, not only the sphenoid sinus, while in OMS, the olfactory function is significantly less dependent on the mucosal thickening of the paranasal sinuses, especially the maxillary sinus. It can be said that volumetric analysis is equally valuable as L-M scoring in the assessment of olfactory disorders. Furthermore, in regards to olfactory test results in both types of sinusitis, olfactory region shading is less influential than the percentage of the obliteration volume and L-M scoring.