A retrospective evaluation was carried out to define the incidence of hydrocephalus and associated factors in 44 patients with Apert syndrome treated at The Hospital for Sick Children in Toronto over a 22-year period. Forty-three of these patients underwent cranioorbital decompressive procedures within 1 year of birth. Fifteen of 25 (60%) patients who had either a computed tomography scan or pneumoencephalogram had ventriculomegaly, and 3 of the 25 (12%) had associated brain anomalies. Ten of the 44 (23%) patients had cerebrospinal fluid (CSF) shunts placed, 7 lumboperitoneal and 3 ventriculoperitoneal. Six of the shunts were placed early after cranioorbital procedures (CSF leaks in 5 cases and a subgaleal fluid collection in 1 case). The average IQ of 15 patients evaluated by the Wechsler Intelligence Scale was 72.5, indicative of significant intellectual impairment. There was no correlation between IQ and ventricular size. Although hydrocephalus characterized by progressive ventricular dilatation is uncommon in Apert syndrome, postoperative problems related to impaired CSF circulation are common and may indicate an underlying CSF absorptive deficit.