The long-term outcome of 39 patients with unruptured giant aneurysm (>2.5 cm) treated during the last 12 years was retrospectively reviewed. The 7 male and 32 female patients, aged 32 to 81 years, presented with symptoms related to compression of the surrounding structures by the aneurysm in 28 cases, cerebral infarction in one, and asymptomatic in 10. The locations were the internal carotid artery (ICA) in 27 cases, middle cerebral artery in three, anterior cerebral artery in one, and basilar artery in eight. Therapeutic modalities were direct clipping in 11 patients, ICA occlusion combined with extracranial-intracranial bypass in 15, and conservative treatment in 13. The follow-up period ranged from 16 to 128 months (mean 54.0 months). The mortality was 9% (1/11), 0% (0/15), and 31% (4/13), and morbidity was 18% (2/11), 20% (3/15), and 8% (1/13), respectively. Surgery reduced the mortality (from 31% to 4%) but increased the morbidity (from 8% to 19%) as compared with conservatively treated patients (p < 0.05). Giant intracranial aneurysm has a poor prognosis if left untreated, but these lesions are difficult to treat with the present management options.