Vascular dementia (VAD) is the second most common cause of dementia. In addition, cerebrovascular disease (CVD) coexists with other causes, including Alzheimer's disease. Cognitive impairment related to CVD may be preventable, and these patients could benefit from therapy. This emphasizes the need for early detection, diagnostic consistency and accuracy of the clinical diagnosis of VAD. A number of current limitations in our knowledge about VAD have restricted the construction of clinical criteria, especially the concept of a behavioral syndrome due to vascular factors affecting the brain, and the main pathophysiological factors related to VAD. The latter include the type, extent, location and tempo of vascular brain lesions, as well as the causality between brain lesions and cognitive impairment. However, relevant information on VAD is beginning to emerge. The NINDS-AIREN Workshop on VAD made an attempt to facilitate international discussion and cooperation by defining consequences of CVD and the criteria for the VAD syndrome, for epidemiological and clinical studies. Here the concepts, pathophysiological factors, current conceptual barriers, and the criteria for the clinical diagnosis are reviewed.