Posttraumatic hydrocephalus is a treatable complication of head injury and can present with several different clinical syndromes. These include obtundation; simple failure to improve; a tetrad of psychomotor retardation, memory loss, gait trouble, and incontinence; and unusual symptoms including emotional disorder. Posttraumatic hydrocephalus seems to result from a blockage of cerebrospinal fluid (CSF) flow around the cerebral convexities. When the lumbar CSF pressure is consistently above 180 mm H2O, the hydrocephalus should be treated unless a contraindication to operation exists. Underlying brain injury from the trauma itself, however, may prevent recovery. When the typical symptoms of normal pressure hydrocephalus (NPH) are present, a shunt is also indicated. Decision-making is difficult when the patient has normal pressure, but is too injured to display the symptoms of NPH or has atypical symptoms. Overnight pressure recording, lumboventricular infusion testing, or cisternography may clarify whether a shunt is needed in this situation, but there is still considerable uncertainty about shunt prediction in this setting.