Clinical, pathological and molecular genetic data are presented in two families in which 15 individuals have developed a progressive dementia. Clinical details are available in 10 individuals, neuropathological data in 2. Affected individuals presented between the ages of 43 and 59 years with personality change or memory loss. All individuals developed a progressive dementia with features of frontal lobe dysfunction. Affected individuals commonly developed additional features which included dysphasia, parkinsonism, limb clumsiness and disequilibrium. Duration to death was between 3 and 13 years. Pathological examination of one individual from each family revealed a combination of features not previously described in a familial dementia. Macroscopic examination revealed lobar atrophy. Microscopy revealed neuronal loss and gliosis with swollen achromatic neurons in the cortex and corticobasal inclusion bodies in the substantia nigra. On clinical assessment these families have many features of Pick's disease but pathological examination reveals features more suggestive of corticobasal degeneration.