Cerebrovascular disease plays an important role in cognitive disorders in the elderly. Cerebrovascular disease and Alzheimer's disease interact on several levels, with one important level being the overlap in risk factors. The major vascular risk factors such as diabetes and impaired glycemic control, hypertension, obesity, and hyper- or dyslipidemia have been associated both with Alzheimer's disease and vascular dementia. The purpose of this review is to consider the context in which vascular dementia is diagnosed, place the pathophysiological consequences of cerebrovascular disease on cognition in the context of clinical and pathological Alzheimer's disease, and then to consider the evidence for the role of major vascular risk factors in late-life cognitive impairment, changes in brain imaging and neuropathological changes. Midlife diabetes mellitus, hypertension, and obesity are established risk factors for clinically defined Alzheimer's disease as well as vascular dementia. The basis for these relationships could either be that the risk factors lead to microvascular brain disease, promote Alzheimer pathology or both. The associations of late-life onset diabetes mellitus, hypertension, and obesity with cognitive impairment are either attenuated or reversed. The role of vascular risk factors in midlife should be the focus of public health efforts to reduce the burden of late-life cognitive impairment.