A 52-year-old female presented with disturbance of consciousness and clinical signs of tentorial herniation. Computed tomography showed a pure acute subdural haematoma (SDH) over the left convexity without subarachnoid haemorrhage. Cerebral angiography showed a saccular aneurysm at the junction of the left internal carotid artery and the posterior communicating artery. Surgery to remove the haematoma and clip the aneurysm showed the rupture point was located in the anterior petroclinoid fold (subdural space). The patient recovered without neurological deficits. Pure SDH caused by ruptured aneurysm is rare. Rupture of an aneurysm adhered to either the dura or falx and located in the subdural space may cause pure SDH. Therefore, ruptured intracranial aneurysm should be considered as a cause of non-traumatic SDH. Immediate removal of the SDH and aneurysmal clipping is recommended in such patients, even those in poor neurological condition.