Traumatic subarachnoid hemorrhage (SAH), a common finding following head trauma, is usually a benign condition with a favorable outcome, seldom requiring surgical intervention. Unlike nontraumatic aneurysmal SAH, most cases of traumatic SAH occur in the sulci of the cerebral convexities, and only rarely arise at the base of the brain. Basal traumatic SAH can be life-threatening and is primarily associated with rupture of vertebrobasilar arteries. We herein present a rare case of basal traumatic SAH resulting from rupture of the posterior communicating artery (PCoA). A 77-year-old male was taken to the emergency department in a semicomatose state. Upon arrival at emergency room, the patient had a Glasgow coma scale (GCS) score of 6 (E1M3V2), and the neurologic examination demonstrated no focal neurologic deficit. Although the trauma history was evident from abrasions and bruising on the face and chest, brain computed tomography (CT) demonstrated basal SAH, which is typical for nontraumatic aneurysmal SAH. Subsequent digital subtraction angiography (DSA) disclosed a traumatic rupture at the mid-portion of right PCoA and ongoing extravasation of contrast media. Despite emergent trapping of the right PCoA by endovascular surgery, the patient's clinical condition only minimally improved. The patient remained bed-ridden with stuporous mentality and persistent hydrocephalus. To the best of our knowledge, this is the first reported case of basal traumatic SAH originating from rupture of the PCoA. This case demonstrates that a meticulous vascular workup is mandatory for every patient with basal SAH, even though a trauma history is clear.