A recently recognised progressive disorder of central myelin in Dalmatian dogs is described. The disease is probably transmitted by autosomal recessive inheritance. The symptoms started at the age of 3-6 months and were dominated by visual deficiency and/or progressive locomotive abnormalities. Pathologically, the most consistent lesions were found bilaterally in the region of the centrum semiovale. The optic nerves were also frequently affected, the basal ganglia and spinal cord were affected infrequently. The main lesions were confined to myelin, while axons and nerve cells were spared, particularly in the early stages of the lesions. Numerous phagocytes were observed which contained engulfed myelin and other lipid breakdown products. Ultrastructurally and histochemically the disease differs from previously described types of leucodystrophy.