The purpose of this study was to examine the height of the main septum (MS) in the sphenoid sinuses and its type, depending on the percentage prevalence of its tissue composition (osseous and membranous) in the adult population. Materials and Methods: A retrospective analysis of 296 computed tomography (CT) scans (147 females, 149 males) of the paranasal sinuses was conducted. The patients did not present any pathology in the sphenoid sinuses. The CT scans of the paranasal sinuses were carried out with a spiral CT scanner (Siemens Somatom Sensation 16) in a standard procedure, in the option Siemens CARE Dose 4D. No contrast medium was used. Having obtained the transversal planes, a secondary reconstruction tool (multiplans reconstruction - MPR) was used in furtherance of gleaning sagittal and frontal planes. Results: In all cases, the height of the MS was measured by using a straight line running parallel to the course of the septum (when the MS was regarded as straight) or curved (when the MS was regarded as irregularly shaped). The average height of the MS was 2.1 ± 0.41 cm in the whole research group. Completely osseous MS was found in 32.77% of the patients. In 63.85% of them, the MS was partially membranous. The rarest was the MS which was not even partially ossified - a membranous type, that was observed in 3.38% of the patients. Conclusions: Variant anatomy of the paranasal sinuses may lead to complications encountered during a surgery, hence a CT scan is advised before the planned treatment.