Objective Large consecutive series on the size and location of ruptured intracranial aneurysms( RIAs) are limited,and therefore it has been difficult to estimate population- wide effects of size-based treatment strategies of unruptured intracranial aneurysms.The authors’ aim was to define the size and location of RIAs in patients diagnosed with subarachnoid hemorrhagedue to aneurysm rupture in a high-volume academic center. Methods Consecutive patients admitted to a large nonprofit academic hospital with saccular RIAs between 1995 and 2009 were identified,and the size,location,and multiplicity of RIAs were defined and reported by patient sex. Results In the study cohort of 1993 patients( 61% women) with saccular RIAs,the 4 most common locations of RIAs were the middle cerebral( 32%),anterior communicating( 32%),posterior communicating( 14%),and pericallosal arteries( 5%). However,proportional distribution of RIAs varied considerably by sex; for example,RIAs of the anterior communicating artery were more frequently found in men than in women. Anterior circulation RIAs accounted for 90% of all RIAs,and 30% of the patients had multiple intracranial aneurysms.The median size( measured as maximum diameter) of all RIAs was 7 mm( range 1 ~ 43 mm),but the size varied considerably by location. For example,RIAs of the ophthalmic artery had a median size of 11 mm,whereas the median size of RIAs of the pericallosal artery was 6 mm. Of all RIAs,68% were smaller than 10 mm in maximum diameter. Conclusions In this large consecutive series of RIAs,83% of all RIAs were found in 4 anterior circulation locations. The majority of RIAs were small,but the size and location varied considerably by sex. The presented data may be of help in defining effective prevention strategies. Objective Large consecutive series on the size and location of ruptured intracranial aneurysms (RIAs) are limited, and therefore it has been difficult to estimate population- wide effects of size-based treatment strategies of unruptured intracranial aneurysms. Authors’ aim was to define the size and location of RIAs in patients diagnosed with aneurysm rupture in a high-volume academic center. Methods Consecutive patients admitted to a large nonprofit academic hospital with saccular RIAs between 1995 and 2009 were identified, and the size, location, and multiplicity Of RIAs were defined and reported by patient sex. In the study cohort of 1993 patients (61% women) with saccular RIAs, the 4 most common locations of RIAs were the middle cerebral (32%), anterior communicating (32%), However, proportional distribution of RIAs varied based on sex; for example, RIAs of the anterior communicatin (14%), and pericallosal arteries Anterior RIAs accounted for 90% of all RIAs, and 30% of the patients had multiple intracranial aneurysms. The median size (measured as maximum diameter) of all RIAs was 7 mm ( For example, RIAs of the ophthalmic artery had a median size of 11 mm, whereas the median size of RIAs of the pericallosal artery was 6 mm. Of all RIAs, 68 % of smaller than 10 mm in maximum diameter. Conclusions In this large consecutive series of RIAs, 83% of all RIAs were found in 4 anterior circulation locations. The majority of RIAs were small, but the size and location varied substantially by sex. presented data may be of help in defining effective prevention strategies.