Current evidence from genetic and epidemiological studies supports the view that Alzheimer's disease (AD) is a heterogeneous disorder. While the disease is pathologically defined by the presence of specified lesions in form of amyloid plaques and neurofibrillary tangles within the parenchyma, other features of pathology are often either neglected or considered coincidental. Our studies suggest that cerebrovascular pathology is inherently part of the disorder, which could be an important factor in a cause or effect manner. We have recently identified subjects having died with severe amyloid beta (A beta) protein cerebral amyloid angiopathy (CAA) in the absence of a profound Alzheimer pathology. These subjects, diagnosed with dementia had a late onset disease and were found at autopsy to exhibit severe CAA but paucity of typical AD changes. Immunocytochemical studies showed numerous microvascular abnormalities as well as characteristic degeneration of the vascular smooth muscle in both surface and intracortical vessels. The pathology was also characterized by occasional intracerebral hemorrhages and multiple infarcts. Further assessment of the abnormalities and amyloid infiltrated cerebral vessels with antibodies to the carboxyl terminus of A beta indicated that the longer, more pathogenic form of A beta(1-42) was found to be highly associated with intracerebral hemorrhages. Our observations suggest that these mild AD cases with a predominantly vascular pathology are variants of AD and bear resemblance to the familial Dutch and Flemish versions of cerebral amyloidosis. We propose that AD is a group of diseases with a variable pathology analogous to the prion diseases, in which a vascular variant also exists.