The frequency of dementia states in old age has been demonstrated and the increasing social medical importance has been focused upon. The discrepant frequency of dementia of cerebrovascular origin between the autopsy and clinical case material and the distinguishing characteristics to the primary degenerative (Alzheimer type) dementia as the most frequent form of dementia have been mentioned. The importance of clinical assessment, apparatus diagnosis and laboratory for the differential diagnosis have been discussed. The importance of the early diagnosis of an underlying vascular etiology for therapy with special attention to prophylactic viewpoints has been emphasized upon.