Abstract： Background:Nontraumatic spontaneous subarachnoid hemorrhage (SAH) is associated with a high mortality.This study was conducted to investigate the epidemiological features of nontraumatic spontaneous SAH in China.Methods:From January 2006 to December 2008,the clinical data of patients with nontraumatic SAH from 32 major neurosurgical centers of China were evaluated.Emergent digital subtraction angiography (DSA) was performed for the diagnosis of SAH sources in the acute stage of SAH (≤3 days).The results and complications of emergent DSA were analyzed.Repeated DSA or computed tomography angiography (CTA) was suggested 2 weeks later if initial angiographic result was negative.Results:A total of 2562 patients were enrolled,including 81.4％ of aneurysmal SAH and 18.6％ of nonaneurysmal SAH.The total complication rate of emergent DSA was 3.9％ without any mortality.Among the patients with aneurysmal SAH,321 cases (15.4％) had multiple aneurysms,and a total of 2435 aneurysms were detected.The aneurysms mostly originated from the anterior communicating artery (30.1％),posterior commtmicating artery (28.7％),and middle cerebral artery (15.9％).Among the nonaneurysmal SAH cases,76.5％ (n =365) had negative initial DSA,including 62 cases with peri-mesencephalic nonaneurysmal SAH (PNSAH).Repeated DSA or CTA was performed in 252 patients with negative initial DSA,including 45 PNSAH cases.Among them,the repeated angiographic results remained negative in 45 PNSAH cases,but 28 (13.5％) intracranial aneurysms were detected in the remaining 207 cases.In addition,brain arteriovenous malformation (AVM,7.5％),Moyamoya disease (7.3％),stenosis or sclerosis of the cerebral artery (2.7％),and dural arteriovenous fistula or carotid cavernous fistula (2.3％) were the major causes of nonaneurysmal SAH.Conclusions:DSA can be performed safely for pathological diagnosis in the acute stage of SAH.Ruptured intracranial aneurysms,AVM,and Moyamoya disease are the major causes of SAH detected by emergent DSA in China.