OBJECTIVE: Aneurysms arising from the internal carotid artery in close relation to the clinoid process have been called paraclinoid aneurysms. The surgical management of these aneurysms poses technical challenges, and such patients are frequently referred for endovascular treatment. We reviewed our experience with endovascular coil embolization of paraclinoid aneurysms to evaluate the safety and efficacy of this treatment modality. METHODS: From December 1993 to May 2002, 70 patients underwent endovascular procedures with detachable coils for 73 paraclinoid aneurysms (8 ruptured, 65 unruptured) at the University of Pittsburgh Medical Center and the University of Texas Southwestern Medical Center. A retrospective review of the medical records, outpatient charts, and operative reports was performed. Angiographic outcome was determined at the end of each procedure and by review of follow-up angiograms. Clinical assessments and outcomes are reported according to the Glasgow Outcome Scale (GOS). RESULTS: Immediate angiographic outcomes for 73 paraclinoid aneurysms demonstrated complete occlusion in 53 (72.6%), near-complete occlusion in 6 (8.2%), and partial occlusion in 14 (19.2%). Nine aneurysms required more than one coiling session to complete treatment; 8 of these aneurysms required two sessions and 1 required four, for a total of 84 endovascular procedures. Follow-up angiograms could be obtained in 49 patients with 52 paraclinoid aneurysms. During the follow-up period; 6 aneurysms demonstrating partial occlusion and 3 demonstrating near-complete occlusion showed spontaneous progression of thrombosis to complete occlusion. Twelve aneurysms initially demonstrating complete occlusion (5 aneurysms), near-complete occlusion (3 aneurysms), or partial occlusion (4 aneurysms) showed coil compaction requiring retreatment. Of these 12 aneurysms that demonstrated coil compaction, 3 were treated with surgery and 9 with coil repacking. The final angiographic outcomes, determined on the last available follow-up angiogram of 49 aneurysms, excluding 3 surgically clipped aneurysms, showed complete occlusion in 43 (87.8%), near-complete occlusion in 3 (6.1%), and partial occlusion in 3 (6.1%). The angiographic follow-up period ranged from 4 to 54 months (mean, 13.9 mo). Morbidity and mortality rates related to 84 endovascular procedures were 8.3 and 0%, respectively. There were no recurrent or new subarachnoid hemorrhages in 63 patients in whom clinical follow-up could be performed during a mean clinical-follow-up period of 14.4 months. The final clinical outcomes demonstrated a GOS score of 5 (good recovery) in 56 patients (88.9%), a GOS score of 4 (moderate disability) in 2 (3.2%), and a GOS score of 3 (severe disability) in 1 (1.6%). Four patients (6.3%) died of unrelated causes. The average period of hospitalization was 17.8 days in patients with acutely ruptured aneurysms and 3.5 days in patients with unruptured or retreated aneurysms. CONCLUSION: The results of this study indicate that endovascular treatment is a safe and effective therapeutic alternative in ruptured and unruptured paraclinoid aneurysms. The endovascular treatment may also confer a positive impact in terms of the length of hospital stay.