Subcortical dementia refers to a clinical syndrome characterised by slowing of cognition, memory disturbances, difficulty with complex intellectual tasks such as strategy generation and problem solving, visuospatial abnormalities, and disturbances of mood and affect. The syndrome was first described by Kinnier Wilson, but further progress in development of the concept has occurred only within the past ten years. Subcortical dementia occurs in degenerative extrapyramidal disorders and has also been identified in inflammatory, infectious, and vascular conditions. Histologic, metabolic, and neurochemical investigations implicate dysfunction primarily of subcortical neurotransmitter systems and subcortical structures or subcortical-frontal connections in the genesis of the syndrome. Subcortical dementia contrasts neuropsychologically and anatomically with disorders such as dementia of the Alzheimer type that affect primarily the cerebral cortex. The clinical characteristics of subcortical dementia reflect the interruption of fundamental functions (motivation, mood, timing, arousal) mediated by phylogenetically and ontogenetically early maturing structures.