In this study an attempt was made to determine the relationship between cerebral amyloid angiopathy (AA) and other cerebrovascular lesions in the aged. The brains of 128 autopsy patients over 60 years of age were examined by both light and electron microscopy. The frequency of cerebral AA increased with age and was 58 percent in patients over the age of 90. The change was observed more often in women than in men. In 7 cases of severe AA, the temporal or occipital cortex was the most common site. Most cases of AA were complicated by the formation of senile plaques in the cortex. Electron microscopic examination revealed amyloid fibrils deposited in clusters in the media and adventitia of the vessels, destroying their structure. Some blood vessels on the surface of the cortex showed hyalinosis, angionecrosis, duplication of the wall, or fibrotic occlusion. AA is sometimes a cause of cerebral bleeding. Five cases of massive cerebral bleeding were found among patients aged 90 or older, including a temporal hematoma in a 92-year-old woman which was believed to be due to the marked AA noted in the temporal lobes. Small cortical infarctions were common in the temporal lobes.