The Hachinski ischemic score (HIS) scale is a simple clinical tool proposed and currently used for differentiating types of dementia (primary degenerative, vascular or multi-infarct, mixed type). Criteria for rating the items of the HIS were never given, or inter-observer reliability in applying it has never been tested. However, the studies which estimated the validity of this scale in predicting the true diagnosis (clinical/CT or neuropathological definition) demonstrated acceptable sensitivity and specificity in defining degenerative or vascular dementia. This scale seems unable to define mixed type dementia or subtypes of vascular dementia. Our review supports the use of the HIS in epidemiological studies on dementia.