There is limited data on the natural history of small intracranial aneurysms. According to the International Study of Unruptured Intracranial Aneurysms, the risk of spontaneous aneurysm rupture is related to aneurysm size and location. ISUIA found aneurysms < 10 mm in diameter, as opposed to aneurysms 10-24 mm and >25 mm, had relative risks of rupture of 11.6 and 59, respectively. Further follow-up from this cohort showed 5-year bleeding risks of 0%, 2.6%, 14.5%, and 40% for aneurysms less than 7 mm, 7--12 mm, 13--24 mm, and 25 mm or greater, respectively. Many other authors (Juvela 2000 and Weir 2002) also suggest the risk of small aneurysm rupture is relatively low. The Sapporo SAH Study group suggests that while the overall rupture risk of small aneurysms is low, the aneurysm size ratio is a strong predictor of aneurysm rupture in small (<5mm) intracranial aneurysms [7]. However, some authors and unpublished data (MUSC) demonstrate that approximately one-third of all ruptured aneurysms are less than 4 mm in size.