Objective: The clinical and pathologic features of hereditary dysphasic disinhibition dementia (HDDD) are described to determine whether it is a variant of known dementias. Background: Several dementing disorders have clinical and pathologic similarities with AD, Pick's disease, and the 'nonspecific' dementias. A detailed description of clinical and pathologic presentation will aid classification, but ultimately the discovery of causative gene(s) will define these disorders. Methods: The authors performed a clinical assessment: gross and microscopic pathologic evaluation of brain tissue, genetic linkage studies, and sequence analyses. Results: HDDD is an autosomal-dominant frontotemporal dementia with many similarities to Pick's disease. Salient clinical features are global dementia with disproportionate dysphasia and 'frontotemporal' symptoms. A linkage between HDDD and 17q21-22 was shown, with a maximum lod score of 3.68 at zero recombination. Conclusions: Several dementias have been linked to the same region and have been termed frontotemporal dementia with parkinsonism linked to chromosome 17. These disorders may represent phenotypic variants arising from mutations within a common gene.