Neuropathological study of the group of presenile dementias, whether apparendy primarily a degeneration of cortical neurones or secondary to vascular, inflammatory or other disease, has for obvious reasons centered on the brain. However, it is possible that the degenerative process may in certain types also affect the peripheral nervous system. If this were so it would be valuable to recognize it not only from the pathological point of view but also, since peripheral nerves are more easily investigated during life, for differential diagnosis which is often difficult and sometimes impossible on clinical findings alone. While involvement of the lower motor neurone is unlikely to be present without causing physical signs impairment of sensation due to involvement of the primary sensory neurone may be overlooked, more especially because sensory testing is often not possible in demented patients.