Subcortical dementia, a concept introduced 20 years ago, is a clinical entity characterized by memory disorders, an impaired ability to manipulate acquired knowledge, important changes of personality (apathy, inertia or depression), slowed thought processes (or bradyphrenia). It is also marked by overwhelming signs of frontal dysfunction. Cognitive and behavioural disturbances are frequently combined to movement disorders (tremor, chorea, dystonia etc). Anatomical, clinical and scintigraphic data suggest that the frontal signs result from a disconnection of the frontal cortex from the basal ganglia. Therefore it is probably more accurate to use the term subcortico-frontal dementia. This pattern of dementia, clearly different from a cortical dementia as dementia of Alzheimer's disease, may be described in a wide range of diseases which mainly involve the subcortical areas: some cases of Parkinson's disease, Progressive Supranuclear Palsy, Huntington's disease, Wilson's disease, the état lacunaire, multiple sclerosis and so on. The concept of subcortical dementia has allowed a better understanding of the role of the basal ganglia and their cortical connections in cognition and behavior. Its neurochemical substrate remains poorly characterized, although the ascending dopaminergic and cholinergic pathways seem to be good candidates, at least in Parkinson's disease.