Although hydrocephalus is a multifactorial disorder, the processes responsible for neurologic impairment can be classified into primary and secondary mechanisms. Primary mechanisms include mechanical compression and stretching of brain parenchyma, ischemia and anoxia, cerebral edema, and blood brain barrier dysfunction. These processes lead to secondary mechanisms, which include cytologic and cytoarchitectural alterations of neurons, reduced size and numbers of cerebral microvessels, axonal degeneration and demyelination, and so on. Shunting studies suggest that neuronal cell death may not play a major role until severe stages of hydrocephalus and that some impairments in connectivity can be reversed. Relatively early shunting may alleviate many of the pathologic features of hydrocephalus, but residual impairments in neurotransmitter levels and dependence on anaerobic respiration leave the treated hydrocephalic brain vulnerable to subsequent insults.