The entity of normal pressure hydrocephalus (NPH) following intraventricular hemorrhage in the newborn has been characterized. Of 87 infants with intraventricular hemorrhage, 20 had early and rapidly progressive hydrocephalus with intracranial hypertension and/or death. In 47 cases there was no increase in ventricular size and in 20 cases there was progressive increase in ventricular size with normal intracranial pressure, ie, NPH. Of these infants with NPH, nine had spontaneous arrest with or without resolution of ventriculomegaly, beginning within 31 days of onset. In 11 cases, after a stable period of NPH lasting 12 to 84 days, there was progressive increase in ventricular size accompanied ultimately by raised intracranial pressure. A relationship between the degree of ventriculomegaly and severity of intraventricular hemorrhage was demonstrated. The data thus define a state of NPH after intraventricular hemorrhage and indicate that approximately half of such cases will not develop progressive hydrocephalus with increased intracranial pressure. If arrest or onset of resolution of ventriculomegaly is not apparent within approximately one month, continued progression and necessity for intervention are to be expected. Serial measurements of intracranial pressure and ventricular size in newborns with posthemorrhagic ventricular dilation allow the diagnosis of NPH and permit early recognition of rapidly progressive ventricular dilation with intracranial hypertension which may follow a stable period of NPH. Such early recognition of this potentially harmful state allows prompt ventricular drainage, thereby preventing brain compression.