Tehran University of Medical Sciences Case Reports in Clinical Practice 2538-2683 7 3 2022 11 02 138 143 EN Abbas Tafakhori Department of Neurology, School of Medicine, Imam Khomeini Hospital Complex, Tehran University of Medical Sciences, Tehran, Iran. Alireza Soltani Khaboushan Department of Neurology, School of Medicine, Imam Khomeini Hospital Complex, Tehran University of Medical Sciences, Tehran, Iran. AND Students’ Scientific Research Center, Tehran University of Medical Sciences, Tehran, Iran. Aydin Taghilou Department of Neurology, School of Medicine, Imam Khomeini Hospital Complex, Tehran University of Medical Sciences, Tehran, Iran. Sajad Shafiee Department of Neurosurgery, Mazandaran University of Medical Sciences, Sari, Iran. 2021 07 07 2021 10 17 A 20-year-old woman presented with left eye ptosis without any headache and pupillary dysfunctions. After the radiological examination, the oculomotor nerve compression was detected in the interpeduncular space by the posterior communicating artery (PCoA) with normal size and shape. The patient underwent frontotemporal craniotomy, and during the surgery, the nerve was detached from the PCoA. Immediately after surgery, all symptoms disappeared. Although oculomotor nerve palsy (ONP) owing to internal carotid-PCoA aneurysm is common, vascular compression due to a non- aneurysmal PCoA is very rare. To the extent of our knowledge, this is the first case in which a slightly displaced, otherwise normal, PCoA causes ONP without any pupillary involvement. After ruling out an aneurysmal artery, this should be considered as one of the possible causes of the ONP. https://crcp.tums.ac.ir/index.php/crcp/article/view/569