About 8-years old boy with a brief clinical history and postmortem findings of a subactue encephalomyelopathy (Leigh-Syndrom) is reported. Pathohistological features were found to be of microcyst formation, vascular proliferation, proliferation of astrocytes, fibrillary gliosis, partial destruction of the myelin sheaths, relative preservation of the cell bodies of neurons. The lesions were symmetrical and involved the tegmentum mesencephali, the lamine quadrigemina, the substantia nigra, the tegmentum pontis, the tegmentum of the medulla oblongata, the basal protion of nucl. lentiformis, the ansa lenticularis, the thalamus, the hypothalamus and the gray matter of the spinal cord. Moderate changes were in the cerebellum. There was no marked histological changes in the cerebral cortex and white matter of the cerebrum, the mammillary bodies, the nervi and tracti optici and the peripheral nerves.