3DCT angiography(3D-CTA), especially multislice helical CT is a noninvasive imaging modality for cerebral aneurysms. 3D-CTA is helpful in the evaluation of the configuration of the aneurysm, the surrounding vessels, and the inside of the aneurysm dome. Clinical application of this technique in complicated large cerebral aneurysms showed that with 3DCT endoscopic imaging, anatomical details of cerebral aneurysms such as the orifice of the aneurysm, intraluminal thrombous, and calcification of the wall could be clearly demonstrated. Using the 3D-imaging method with helical CT, virtual views of various surgical approaches can be compared preoperatively. This information was found to be very useful for determining difficult aneurysms for coil embolization or direct surgery including complication and broad-based aneurysms.