A 79 years-old man suffered gait disturbance for more than ten years. During the last year the gait worsened. Twenty days after having developed a right hemiparesis, he died from cardiorespiratory failure. Neurological signs were characterized by cogwheel rigidity, distal paresis and amyotrophy of the legs. E.M.G. demonstrated a denervation; ulnar conduction velocity was 38 m/s. The sural nerve biopsy showed a loss of myelinated fibres and no onion-bulb-like formations. A sister (72 years) and two nephews (51 and 39 years) also suffer gait disturbance. The E.M.G.'s demonstrate denervation of the legs. The amplitudes of the motor and sensory nerves are reduced and conduction velocities range between 39 and 59 m/s. Pathologic examination of the propositus showed recent left frontal subcortical infarction, partial neuronal depopulation of the substantia nigra and Lewy inclusions. Microscopic examination of the spinal cord showed integrity of the posterior columns, anterior and posterior spinal roots, cauda equina, and of a thoracic posterior root ganglion. The anterior horns showed a mild gliosis and a slight neuronal depopulation with a few pale or atrophic neurons and very rare neuronophagias. This is believed to be the first autopsy report of a dominant sensory motor neuropathy of the neuronal type. The relative integrity of the spinal cord suggests that the peripheral motor and sensory neurons are affected to the greatest degree at their distal extremity.