The subcortical dementias such as progressive supranuclear palsy, Huntington's disease, and Parkinson's disease are said to be characterized by the presence of slowed mentation, apathy, and the absence of aphasia, agnosia, and apraxia, symptoms that are claimed to be more common in cortical dementias such as Alzheimer's disease. Conceptual problems (such as vagueness of terms and difficulties with symptom definition) and methodological problems (such as improper matching of comparison groups and inadequate assessment techniques) found in currently available studies require a reappraisal of this classification of dementias into cortical and subcortical forms. A review of recent clinical, neuropathological, and neurochemical studies offers little support for this classification system, although adequate systematic studies have not been performed.