Four autopsy cases of porencephaly and hydranencephaly were evaluated clinico-pathologically. The patients showed profound mental retardation, convulsive seizures and spastic quadriplegia. The life spans were much shorter in the hydranencephalic cases. Pathologically, the cerebral cortex in the vicinity of the parenchymal defects often showed an abnormal cytoarchitecture, which appeared to be closely correlated with superficial glial proliferation. Several neurofibrillary tangles were found in the nucleus basalis of Meynert and the locus ceruleus in a 23-year-old porencephalic patient, and so-called grumose degeneration of the dentate nucleus in three patients, including a 2-month-old hydranencephalic boy. It is suggested that extensive cerebral defects may cause neuronal degeneration of the subcortical nuclei.