OBJECTIVE: To study clinical outcome of giant intracranial aneurysms (diameter >= 25 mm) treated with different surgical modalities and to analyze factors affecting prognosis. METHODS: A retrospective analysis was performed of 204 consecutive patients with giant intracranial aneurysms who underwent surgical treatment in our department from 1995 to 2008. Clinical outcome was evaluated with the Glasgow Outcome Scale. RESULTS: Surgical modalities included direct aneurysm neck clipping in 102 patients (50.0%), parent artery reconstruction in 51 patients (25.0%), proximal artery ligation in 23 patients (11.3%; 4 patients combined with revascularization), trapping in 26 patients (12.7%), and wrapping in 2 patients (1.0%). Follow-up data were available for 181 patients (88.7%), with a mean follow-up period of 62 months (range, 12-164 months). A good outcome (Glasgow Outcome Scale score 5) was observed in 114 patients (63.0%), and a poor outcome (Glasgow Outcome Scale score 1-4) was observed in 67 patients (37.0%). Independent factors that affected prognosis were age and location of aneurysm. Older age (>= 50 years) and location of aneurysm in posterior circulation were associated with poor outcome. In 85 patients with preoperative subarachnoid hemorrhage, patients with a higher Hunt and Hess grade (>= 3) had a worse outcome compared with patients with a low Hunt and Hess grade (1 or 2). Surgical modalities and other factors were not significantly associated with clinical outcome. CONCLUSIONS: Giant intracranial aneurysms are effectively treated with craniotomy and surgical treatment. Older age, aneurysm location in posterior circulation, and higher Hunt and Hess grade are risk factors affecting prognosis.