Hereditary dysphasic dementia is described in terms of its clinicopathological, ultrastructural, and transmissibility characteristics. Its mode of inheritance is autosomal dominant, and its clinical manifestations of progressive dementia and severe dysphasic disturbances are expressed in late adulthood. Complete neuropathological examination of four patients reveals findings typical for Pick's disease (asymmetrical focal cerebral atrophy), Alzheimer's disease (profuse neuritic plaques), and paralysis agitans (neuronal depigmentation, depletion, and Lewy body formation in substantia nigra) in addition to a striking but nonspecific spongiform degeneration of superficial cortical layers. This unique combination of gross morphological and histopathological features qualifies hereditary dysphasic dementia as a distinct entity, but its precise relationship to the well‐recognized adult cortical dementias has been difficult to establish by conventional classification methods. This disorder and other unusual dementing illnesses may be best considered as part of a Pick‐Alzheimer spectrum of cortical neuronal degenerations.