Paraclinoid internal carotid artery aneurysms are difficult to treat and difficult to visualize by using DSA, MRA, or surface-rendered 3D-CTA. Because those aneurysms are surrounded by bone, the dural ring (proximal and distal), the optic nerve, the oculomotor nerve, and the cavernous sinus. This report represents the first attempt to assess the verification of volume-rendered 3D-CTA for surgical planning in treating paraclinoid internal carotid artery aneurysms. From January, 1996 to October, 2001, we treated 15 cases of unruptured paraclinoid internal carotid artery aneurysms at Kobe University Hospital. Twelve of the patients were women and three were men, ranging age from 33 to 70 (55.7 /10.3). We studied used volume-rendered 3D-CTA to examine five patients and surface-rendered 3D-CTA for ten. Volume-rendered 3D-CTA allowed observation of the aneurysms and their necks and the surrounding structures in all cases (P<0.001), while surface-rendered 3D-CTA allowed partial observation of the aneurysms in 5 cases (50%). Volume-rendered 3D-CTA enabled virtual removal of bones by using the clip-plane editing and allowed the aneurysms to be viewed from various angles. When the pterional approach is used and the neck of the aneurysm is found to be remote from the anterior clinoid process, the anterior clinoid process need not be removed. In conclusion, for paraclinoid internal carotid artery aneurysms, volume-rendered 3D-CTA is superior to surface-rendered 3D-CTA, MRA and digital subtraction angiography in terms of visualization of the aneurysm and surrounding bones. It was great help for surgical planning in treating paraclinoid internal carotid artery aneurysms.