Cognitive decline is a central component of the dementia process. Population-based prospective studies have confirmed the existence of age-related cognitive decline, although its conceptual basis and nosological status remain controversial. Healthy old people show decline with aging in global cognition and memory function in particular. Preclinical and clinical dementia patients exhibit deficits across multiple cognitive domains, with the largest and most consistent deficits in memory function. Cerebrovascluar disease may lead to cognitive decline and promote the clinical expression of dementia directly or by interaction with APOE η4. Early treatment and prevention of cerebrovascular disease may be the major measures for preventing and postponing the progression of the vascular disease related cognitive decline.