BACKGROUND Perimesencephalic nonaneurysmal subarachnoid hemorrhage (PNSH) appears to have an origin and natural history distinct from aneurysm rupture. However, the risk factors and complications of this pattern are still in debate. We performed a study with goals of comparing PNSH risk factors and clinical presentations with other sorts of spontaneous subarachnoid hemorrhages (SAH) and exhibit the PNSH outcome and prognosis. METHODS Retrospective review of patients who experienced SAH between May 2006 and July 2008 in the First Affiliated Hospital of Chongqing Medical University was undertaken. Patients were categorized as perimesencephalic nonaneurysmal subarachnoid hemorrhage (PNSH), nonperimesencephalic nonaneurysmal subarachnoid hemorrhage (NPNSH), aneurismal subarachnoid hemorrhage (ASH), and uncertain SAH of which the patterns were not clear. The possible risk factors and clinical presentations within the three groups were used to proceed for statistical analysis. RESULTS A total of 159 residents were identified. Among of them, 12 patients had the perimesencephalic pattern. Patients with PNSH showed less likelihood with the female (P=0.029), alcohol consumption (P=0.033), hypertensive (P=0.005), diabetes (P=0.013) or hyperlipidemia (P=0.034) when compared with aneurismal SAH. The clinical presentations of this pattern showed less conscious disturbance (P=0.004), vomiting (P=0.005), or poor Hunt & Hess Grade (P=0.003). There was one death among PNSH patients during 12 months mean follow-up. CONCLUSIONS Patients with PNSH present better clinical course than other forms of SAH, which could assist the diagnosis of this pattern. The moderate clinical course may suggest clinician apt to exclude aneurysm rupture. However, similar presents in remaining nonaneurysmal subarachnoid hemorrhage might suggest benign entities in other forms of nonaneurysmal subarachnoid hemorrhage.