Background.Arterial bifurcations are sites of maximal hemodynamic stress, where cerebral aneurysms commonly develop.However, in our experience with endovascular treatment and surgery treatment for aneurysms of the internal carotid artery (ICA) bifurcation, we often experienced that the aneurysmal neck did not necessarily exist only at the ICA bifurcation (ICBi), but often at the apex of the outer (lateral) wall of the curved anterior cerebral artery.In this study, we have retrospectively evaluated the hemodynamic stress characteristics of aneurysms at the ICBi.Methods.Eighteen ICBi aneurysms in 18 consecutive patients were studied retrospectively.The size of the aneurysms, the vessel curvature of the the anterior cerebral artery (ACA) and middle cerebral artery (MCA), and the diameter of the ACA and MCA were measured.Furthermore, to study the relationship between the location of the aneurysmal neck and the bifurcation of the ICA, the distance between the midline of the aneurysmal neck and the apex of the internal carotid artery bifurcation was measured.Results.The average aneurysm size was 5.74±2.91mm and the average neck was 2.51 ± 1.07mm.The curvature of the ACA was significant bigger than of the MCA.The average diameters of the ACA and MCA were 2.22 ± 0.37 mm and 2.93 ± 0.51 mm, respectively.The average distance between the midline of the aneurysmal neck and the ICA was 1.72 ± 0.79mm, and almost aneurysmal necks of the ICBi arose from the side of the ACA.Conclusion.ICBi aneurysms were deviated to the side of the A1 segment of the ACA, where the artery might suffer higher hemodynamic stress.Our preliminary results indicate that the high wall shear stress is the key factor for the formation snd development of intracranial aneurysms srised from curved anterior cerebral arteries.