In a longitudinal prospective study of dementia, 158 patients were investigated post mortem. Sixteen patients were classified as frontal lobe dementia (FLD) of non-Alzheimer type and four cases as Pick's disease. Positive heredity for dementia was reported in 50% of these cases compared to 30% in a reference group of patients with Alzheimer's disease (AD). The typical clinical picture in FLD and Pick's disease was that of a slowly progressive dementia, at an early stage dominated by personality change, lack of insight, disinhibition, and later on stereotypy and increased apathy. There was also a progressive dynamic aphasia ending in mutism and amimia. Memory and spatial functions were comparatively spared. Disinhibition, oral/dietary hyperactivity, and echolalia were more consistently found in Pick's disease compared to FLD. The differential diagnosis against AD, cerebrovascular dementia, and other degenerative dementias and against affective disorders and psychotic reactions are discussed.