A family is described in which affected members have clinical features consistent with the late onset form of Strümpell's Familial Spastic Paraplegia which is of dominant inheritance. Abnormalities in cortical somatosensory to peroneal nerve stimulation were found in all affected members of the family and in several who were clinically unaffected. In some cases responses were better defined at slow rates of stimulation. Peripheral nerve conduction velocity was normal. These changes are consistent with previous findings of degeneration in the posterior columns at necroscopy and with a dying back process in the first sensory neuron. Clinically unaffected members of the family with abnormalities in the somatosensory response may represent asymptomatic heterozygotes.