The ultrastructural pathology of cerebral cortex in human hydrocephalus is reviewed and compared with experimental hydrocephalus. Nerve cells show moderate and severe swelling. The neighboring neuropil exhibits notable enlargement of extracellular space, synaptic plasticity and degeneration, damage of myelinated axons, and myelination delay. The astrocytes display edematous changes and phagocytic activity. Glycogen rich- and glycogen-depleted astrocytes are observed. Some oligodendroglial cells exhibit normal morphology, and other exhibit hydropic changes. The capillary wall shows signs of blood-brain barrier dysfunction. The role of ischemia, oxidative stress, increased calcium concentration, activation of NMDA receptors, and disturbance of ion homeostasis are discussed in relationship with the fine structural alterations of hydrocephalic brain parenchyma.