In infancy, the intracranial pressure (ICP) is normally maintained at a level that is very low by standards that apply later in life. There is little or no overlap of normal pressure and the pressure in infantile hydrocephalus. Knowledge of the normal pressure may allow expectant management of milder instances of infantile hydrocephalus. During the first few days after birth, as the volume of the brain decreases so does its turgor, and subatmospheric ICP is common. Hydrocephalus may be masked or attenuated in severity during that time or may be incorrectly suspected in a normal child because of the increase in circumference of the head accompanying the restitution of volume. The postnatal decrease in ICP may be responsible for ventricular hemorrhage in the newborn.