Vascular dementia (VaD) is the second most common cause of dementia. In addition, cerebrovascular diseases (CVD) coexist with other causes of dementia. Cognitive impairment related to CVD may be preventable and these patients could benefit from therapy, which emphasizes the importance of early detection and accurate diagnosis of VaD. The conventional concept of VaD is that of multi-infarct dementia (MID). However, VaD is not only MID; it relates to different vascular mechanisms and different changes in the brain, and has different clinical manifestations with different causes. Critical conceptual questions include the cognitive syndrome and the vascular causes. It is unclear whether the conventional concept of dementia is appropriate or should be substituted with a milder and broader definition, such as vascular cognitive impairment. Furthermore, there is confusion about the causes, especially the role of lesion characteristics and the noninfarct factors. The current diagnostic criteria for VaD are based on the infarct concept. The NINDS-AIREN criteria include dementia, CVD, and a relationship between these two disorders. The criteria define the CVD and the relationship between dementia and CVD, and list supporting clinical features for the diagnosis of VaD, as well as features that make the diagnosis uncertain. The interrater reliability of these criteria is moderate to substantial (κ .46 to .72). The expected antemortem accuracy using these criteria approaches 90%. The challenge is to correctly diagnose combined cases with both vascular and Alzheimer-type pathology. Main tools in the diagnosis include a detailed medical history, neurological examination, clinical or neuropsychological mental status examination, and basic laboratory examinations. Brain imaging should always be performed, preferably using magnetic resonance imaging. The diagnosis, especially in early cases, is usually made by a neurologist. The challenge for the primary care physician is to identify the early cases needing further examinations and organizing treatment and follow-up after diagnosis.