A histological study of a peculiar progressive disease of the central nervous system (CNS) named amyotrophic leukospongiosis was carried out in 5 observations. The regular histological signs included the loss of motor neurons in the spinal cord and encephalon, the status spongiosus of the white matter in the anterior and lateral columns of the spinal cord and different parts of the white matter in the encephalon. Unlike amyotrophic lateral sclerosis, amyotrophic leukospongiosis is characterized by intact myelin fibers of the anterior and lateral columns (including pyramidal tracts). The clinical, epidemiological, and histological data allow the disease to be classified into the group of slow virus infections.