We reviewed and compared the clinical course and long-term prognosis of patients with non-aneurysmal subarachnoid hemorrhage (SAH) with and without a perimesencephalic pattern of hemorrhage on CT scan. In 876 patients with spontaneous SAH, 52 (5.9%) were diagnosed with non-aneurysmal SAH. Based on their CT scans, the SAH was classified as perimesencephalic non-aneurysmal SAH (PNSH) in 23 patients and non-perimesencephalic (non-PNSH) in 29 patients. The patients in the non-PNSH group were further divided into diffuse type (19 patients) and localized type (10 patients). We performed follow-up three-dimensional-CT angiography (3D-CTA) in all possible patients at least 1 year after the attack. The PNSH group had a lower rate of acute hydrocephalus (8.7%) and angiographic vasospasm (0%) complications than the non-PNSH group (37.9% and 27.6%, respectively). Only one case of rebleeding occurred in the non-PNSH group. No demonstrable source of bleeding was found on follow-up 3D-CTA, which was performed 1 year after the attack. All patients with non-aneurysmal SAH had similarly favorable long-term functional outcomes. Based on our study, patients with non-PNSH have a more complicated clinical course than those with PNSH. However, the long-term prognosis was similarly favorable for both the PNSH and non-PNSH in limited circumstances when they showed normal findings on a series of two-dimensional and 3D angiographic work-ups.