Ischemic vascular disease (IVD) is the second most common cause of dementia in the Western world. This article focuses on dementia resulting from subcortical ischemic vascular disease (SIVD), a subtype of IVD, which in many cases may be prevented. Hypertension and diabetes are the leading causes of small-artery disease, subcortical brain ischemia, and stepwise or slowing progressive decline in cognitive function. The pattern of cognitive impairment in SIVD, as compared with Alzheimer's disease, is characterized by greater impairment of executive function but better preservation of recognition memory. Structural neuroimaging studies, such as computed tomography and especially magnetic resonance imaging, are more sensitive than the clinical examination and can enable detection of subcortical lacunes and deep white matter changes that are clinically silent. Often the brain can be protected against SIVD by early diagnosis and management of risk factors. Once end-organ damage has occurred, however, treatment outcome is less satisfactory. The most common risk factors for SIVD--hypertension and diabetes mellitus--are best detected and managed in primary care settings.