Background and Purpose-Although results of the randomized International Subarachnoid Aneurysm Trial suggested that coil embolization was superior to surgical clipping 1 year after treatment, a paucity of data on long-term outcomes has been a major concern. Methods-In an ambidirectional cohort study, 9 institutions with expertise in intracranial aneurysm treatment identified all ruptured saccular aneurysms treated 1996 to 1998. After an initial medical record review, all patients meeting entry criteria were contacted by postal questionnaire or telephone. Possible reruptures were adjudicated independently by a neurologist, a neurosurgeon, and a neurointerventional radiologist. Rates of delayed (Ͼ1 year) and early rerupture and retreatment were evaluated using Kaplan-Meier survival analysis and the log-rank test. Results-A total of 1010 patients (711 surgically clipped, 299 treated with coil embolization) were included. Patients treated with coil embolization were older, more likely to have smaller aneurysms arising from the posterior circulation, and less likely to have middle cerebral artery aneurysms. Rerupture of the index aneurysm after 1 year occurred in 1 patient treated with coil embolization during 904 person-years of follow-up (annual rate 0.11%) and in no patients treated with surgical clipping during 2666 person-years (Pϭ0.11). Aneurysm retreatment after 1 year was more frequent in patients treated with coil embolization (PϽ0.0001), but major complications were rare during retreatment. Conclusions-Rerupture of aneurysms treated by either coil embolization or surgical clipping is rare after the first year.Late retreatment is more common after coil embolization than after clipping but complication rates are low. Thus, late events are unlikely to overwhelm differences between procedures at 1-year follow-up.