We investigated consecutive 1000 autopsied cases (average age 82.9 years) clinicopathologically in order to reveal the significance of cerebral amyloid angiopathy (CAA) as a cause of senile intracranial hemorrhages. We found 101 cases with intracerebral hemorrhages, and CAA accounted for 10.9% of them (31.0% of lobar cerebral hemorrhages, and 14.3% of cerebellar ones). In contrast to hypertensive hemorrhages, CAA-related ones (1) ruptured into the subarachnoid space without exception, (2) often coexisted with dementia of Alzheimer's type, and (3) frequently occurred in the night without elevated blood pressure at onset. The cerebrovascular amyloid was strongly immunoreactive with antibody to beta-protein in all of the cases with CAA-related hemorrhages, and less intensively with antibody to cystatin C in 91% of them. Our data indicate that CAA is an important etiological factor of cerebellar hemorrhages, as well as lobar cerebral hemorrhages, in normotensive, aged patients.