Abstract: Objective:To investigate the value of CT angiography(CTA) in the etiological diagnosis of spontaneous subarachnoid hemorrhage(SAH) with 64-slice CT.Methods:from January to December 2009,97 patients with spontaneous subarachnoid hemorrhage underwent CTA with 64-slice CT,post-processing techniques such as volume rendering(VR),maximum intensity projection(MIP),curved planar reformation(CPR),multiplanar reformation(MPR) were used to show blood vessels with a clear cause.Results:CTA diagnosis of 12 cases of normal,one case of carotid cavernous fistula,nine cases of arterioven- ous malformation,75 cases of aneurysm,all patients were confirmed with digital subtraction angiography(DSA) and or surgery,12 normal cases diagnosed by DSA,64-slice CTA missed one case,but the overall sensitivity of 98.7 % and specificity of 100%.Conclusion:64 slice CT angiography is a simple,rapid,minim-ally invasive,safe and economical method in the diagnosis of the cause of spontaneous subarachn-oid hemorrhage with a high accuracy,it can be used as a preferred method in the early etiological diagnosis of spontaneous subarachnoid hemorrhage.