Aim:For endovascular embolization of paraclinoid aneurysms, superselection needs consideration of the complex anatomy around the carotid siphon. As no guideline or classification has been established for selecting proper microcatheters, pre-shaped microcatheters must be considered. We suggest a geometric classification of paraclinoid aneurysms for microcatheter selection.Material and Methods:Clinical data from 76 patients (80 paraclinoid aneurysms) who underwent endovascular treatments were retrospectively reviewed. Paraclinoid aneurysms were classified according to the six directions where the aneurysm neck lies and simplified into three groups as follows: superior, medial, and lateral groups. The medial group was further divided into proximal, mid, and distal subgroups according to the location of the aneurysm neck on lateral angiography. Furthermore, we assessed the superselection success rate with the first-selected pre-shaped microcatheter per group.Results:According to the aneurysm direction, the medial group showed relatively lower superselection success rates (66.1%) than the superior (81.8%) and lateral groups (85.7%). The S-shaped microcatheter was the most frequently used in the superior (69.2%) and lateral groups (62.5%). Acute-angled J- and C-shaped microcatheters (88.5%) were preferred for proximal aneurysms; and obtuse-angled 45- and 90-angled microcatheters (75%), for distal aneurysms. The mid-portion group showed the lowest success rate (45.8%) and more difficulties in pre-shaped microcatheter superselection.Conclusion:Medially directed mid-portion aneurysms were difficult to access using pre-shaped microcatheters; thus, tailored steam-shaping techniques may be considered. Superiorly and laterally directed aneurysms could be accessed using pre-S-shaped microcatheters. Acute-angled microcatheters may be considered for proximal aneurysms; and obtuse-angled microcatheters, for distal aneurysms.