Optimal cognitive function is vital to independence, productivity, and quality of life, and the debilitation associated with dementias makes them the most feared of conditions related to aging. Effective preventive measures are key components of any response to the potentially overwhelming problem of dementias. Increasing evidence points to the potential risk roles of vascular factors and disorders (eg, midlife obesity, dyslipidemia, diabetes, high blood pressure, cigarette smoking, and cerebrovascular lesions) and the potential protective roles of psychosocial factors (eg, higher education, regular exercise, healthy diet, intellectually challenging leisure activities, and active socially integrated lifestyle) in the pathogenic process and clinical manifestation of dementing disorders. Optimal control of vascular risk factors, secondary prevention of stroke, and manipulation of lifestyle factors have demonstrated efficacy in prevention of stroke and myocardial infarction. Thus, adding dementia prevention and brain function preservation as goals to already existing or planned prevention efforts is appropriate and necessary. Age must be taken into account when assessing the likely effect of such interventions against dementia, which underscores the need to begin prevention efforts early in patients' lives.