A 53 year old man developed symptoms of motor neuron disease in childhood. There was a family history of a similar disorder and it was felt to represent a form of Kugelberg-Welander disease. In addition to the motor deficits, sensory abnormalities in his legs were documented during life. Autopsy revealed anterior horn cell loss throughout the length of the spinal cord, with preservation of the phrenic nucleus. The lumbar dorsal root ganglia showed active degeneration of sensory neurons, with nuclear changes exceeding cytoplasmic ones. The fasciculus gracilis showed Wallerian degeneration. The findings provide direct evidence that sensory neurons can degenerate in some forms of motor neuron disease, and that the "demyelination" or "degeneration" of posterior columns sometimes seen in the various forms of motor neuron disease may actually be secondary to cell body disease in the dorsal root ganglia.