The findings are described in an adult case of metachromatic leukodystrophy examined by light, polarization and electron microscopy. Symmetrical demyelination was found in the cerebral hemispheres, but was moderate in the cerebellum, brain stem and spinal cord. Early changes in myelin of peripheral nerves have been demonstrated by polarization microscopy. Various metachromatic structures have been described in glial cells and neurons by electron microscopy, indicating disturbances at different metabolic steps of lipid metabolism. There are minor but no essential ultrastructural differences in the disease of different ages.