All 49 members of four generations of a family were identified. In the first three generations eight members were afflicted with dementia, whereas in the fourth generation only one was demented but three of four were afflicted with motor neuron disease and they also had slight cognitive deficiencies. The pattern of heredity is compatible with dominant autosomal inheritance. Neuropsychological testing revealed affection mostly of the frontal lobes. A pedigree and six case reports are presented.