Arterial stiffness constitutes a reduction in the ability of large arteries to readily accommodate the increase in blood ejected from the heart during systole. Propagation of the pulse wave or pulse wave velocity (PWV) is a relatively simple, non-invasive, and reproducible method to determine arterial stiffness. There is mounting evidence that consistently implicates arterial stiffness in the pathogenesis of impaired cognitive function and dementia in the elderly. This paper summarizes this evidence. First, the majority (85%) of the twelve studies comprising over 6,000 individuals found a significant association between increased vascular stiffness and cognitive impairment in multivariate analysis after adjusting for age, educational level, and other factors that influence cognition. Second, higher pulse wave velocity, adjusted for age and other factors, was associated with a greater amount of white matter hyperintensities on brain imaging, indicating cerebral small-vessel disease. Third, studies consistently indicate that higher PWV is a significant predictor of subsequent cognitive decline. Fourth, some data support the proposition that arterial stiffness (PWV) increases progressively from persons with normal cognitive function to those with mild cognitive impairment, to Alzheimer's disease, and then to vascular dementia. Fifth, there is some suggestion that antihypertensive drugs that have a more favorable effect to reduce vascular stiffness are more likely to reduce the occurrence of cognitive impairment. Taken together, these data suggest that artery stiffness may be a useful clinical tool to detect individuals at risk for cognitive impairment and dementia of the elderly.