The concept of Vascular Cognitive Impairment (VCI) encompasses patients across the entire continuum of cognitive impairment resulting from cerebrovascular disease (CVD), ranging from high-risk patients with no frank cognitive deficit (the "brain-at-risk" stage) through vascular dementia (VaD). There are accepted differences in the neuropsychological profile of patients with Alzheimer's disease (AD) and VaD. In patients with VaD, executive functions that tend to be disproportionately impaired include planning and sequencing, speed of mental processing, performance on unstructured tasks, and attention. Language production may be impaired in patients with VaD but primary language functions otherwise tend to be preserved. Patients with VaD also exhibit significantly more perseverations than patients with AD. Memory impairment is typically evident in patients with AD+CVD but memory impairment may also occur as a primary consequence of stroke in the posterior cerebral artery territory with involvement of the medial temporal lobe, or as a secondary consequence of a cognitive syndrome involving inattention due to primary executive dysfunction. Compared to VaD, patients with AD may exhibit greater deficits in functions (including memory) mediated by posterior cortical structures, such as the temporal and parietal lobes. AD patients exhibit a faster rate of information decay, reduced ability to benefit from cues to facilitate retrieval, and higher frequency of intrusion errors; in addition, certain aspects of language function, such as naming, may exacerbate deficits on verbal memory tasks. AD tends to affect lexicon while VaD tends to affect syntax. When patients with AD exhibit perseverations, they tend to be elicited by tests of semantic knowledge.