Patients born with craniofacial syndromes such as Crouzon's syndrome will often develop hydrocephalus after their initial craniofacial reconstructive procedures. We have treated 10 patients with Crouzon's syndrome; 5 patients required a shunting procedure after cranial remodeling. Each of these 5 shunted patients later demonstrated chronic tonsillar herniation on magnetic resonance imaging studies. One of these patients exhibited signs of pseudotumor cerebri and 1 had a spastic quadriparesis. Of the 5 patients who did not require a shunt, none displayed chronic tonsillar herniation. Our evidence suggests that jugular foramen stenosis produces an increased cerebral venous turgor that leads to a cerebrospinal fluid absorption defect and hydrocephalus. After the hydrocephalus is treated the increased venous turgor remains and provides the driving force for the development of chronic tonsillar herniation.