A neuropathological study of a case of Menkes disease is reported, illustrating the involvement of different types of neuronal cells. The cerebellum showed the most striking abnormalities: severe lack of internal granule cells. Purkinje cells with weeping willow pattern, numerous segmental enlargements of dendritic trunks and secondary branches, and presence of numerous eosinphilic spherical bodies in the molecular layer were the most conspicuous features. Using electron microscopy, the dendritic enlargements were observed to be made of both proliferated and enlarged mitochondria, and of saccules of smooth endoplasmic reticulum. The spheroid bodies in the molecular layer were mainly made of concentric lamellar structures which seemed to be proliferated smooth endoplasmic reticulum. The relationship between these morphological abnormalities and the metabolic disorder of Menkes disease is discussed.