Background: It is uncertain whether the location and size of a ruptured intracranial aneurysm (IA) independently influences the outcome of subarachnoid hemorrhage (SAH). Objective: To determine the independent relationship of location and size of a ruptured IA with serious clinical outcomes after SAH in an Australasian population-based study. Methods: From 432 first-ever cases of primary SAH registered prospectively over 12 months in 4 Australasian cities between 1995 and 1998, the demographics, clinical features, risk factors and results of investigations were obtained, including the location and size of any ruptured IA as assessed by cerebral angiography, computed tomography and/or magnetic resonance imaging. Location was classified as either anterior (i.e. anterior communicating artery, internal carotid artery and middle cerebral artery) or posterior circulation (i.e. posterior communicating artery, posterior inferior cerebellar artery, basilar artery and vertebral artery), and size was classified as <5, 5-9 and ≥10 mm. Outcomes recorded during hospitalization were rebleeding, delayed ischemia, hydrocephalus, residual neurological impairment and in-hospital death. Logistic regression analysis was used to evaluate the effects of IA location and size on outcome, independent of other potential prognostic factors. Data are reported with odds ratios (OR) and 95% confidence intervals (CI). Results: IA location and size were confirmed separately in 299 and 252 patients, respectively. Patients with a posterior circulation IA had a lower rate of rebleeding than those with an anterior circulation IA (adjusted OR: 0.11; 95% CI: 0.02-0.87), but otherwise there was no significant relationship between IA location and outcome. Patients with a larger ruptured IA had higher risks of rebleeding (p = 0.02 for trend) and in-hospital death (p = 0.001) after controlling for age, sex, ethnicity, location of the ruptured IA and neurosurgical intervention. Conclusion: IA location in the posterior circulation was associated with a lower risk of rebleeding than IA in the anterior circulation. A larger IA size was associated with higher risks of rebleeding and in-hospital death.