The aim of this study was to investigate the neurovascular structures of the cavernous sinus with the endonasal endoscopic transpterygoid approach on fresh human cadavers. Additionally, the course of internal carotid artery (ICA) and relevant anatomy was thoroughly investigated to refine the anatomical landmarks, exposure difficulties, potential complications, and limitations using the endonasal endoscopic technique. This study was carried out at an otolaryngology department of a tertiary medical center between June 2014 and June 2015. The surgical dissection was performed on 10 fresh human cadaver specimens using paranasal sinus and skull base endoscopic instruments. Cavernous sinuses and parasellar area were explored via an endoscopic endonasal transpterygoid approach. Dehiscence was present in 5 (25%) cavernous ICAs. Projection of the cavernous ICA on the whole lateral sphenoid wall was prominent in 6 (%30) sphenoid sinuses. Anterior curve was prominent in 12 (60%) cavernous ICAs, whereas posterior was prominent in 7 (35%). Mean distance between the lateral wall of eustachian tube orifice and petrous ICA was 19.50 ± 1.05 mm (range 18-22 mm). Cranial nerves of the cavernous sinus showed no variation. Control of the ICA is critical during the endonasal endoscopic approach to the cavernous sinus and skull base. The vidian nerve is a reliable and important landmark to the petrous ICA in the transpterygoid approach. Dissection of the eustachian tube and its relation to the ICA has to be kept in mind during nasopharyngeal surgery.