Inherited deficiency for the lysosomal enzyme arylsulfatase A (ASA) leads to lysosomal storage of sulfatides and to dramatic demyelination in the CNS of humans (metachromatic leukodystrophy, MLD). As an animal model, ASA(-/-) mice have previously been generated by disruption of the ASA gene and are known to develop lysosomal sulfatide storage similar to that in human MLD, and, moreover, to become deaf because of degeneration of the primary neurons of the auditory pathway. The present study deals with the cellular and topographic distribution of sulfatide storage throughout the CNS of ASA(-/-) mice between a few days and 24 months of age. Sulfatide accumulation was detected on the ultrastructural level and by histochemical staining with alcian blue. Sulfatide storage was found in oligodendroglia and neurons in young mice, and in activated microglia (phagocytes) in adult mice. Neuronal sulfatide storage was most prominent in many nuclei of the medulla oblongata and pons, and in several nuclei of midbrain and forebrain. Sulfatide-storing phagocytes were most frequent in the white matter tracts of aged ASA(-/-) mice, whereas no widespread demyelination was obvious. Loss of neurons was found in two nuclei of the auditory pathway of aged ASA(-/-) mice (ventral cochlear nucleus and nucleus of trapezoid body). The distributional pattern of sulfatide storage throughout the CNS of ASA(-/-) mice largely corresponds to data reported for human MLD. An important difference, however, which remains unexplained at present, is the absence of obvious demyelination from the CNS of ASA(-/-) mice up to the age of 2 years.