Continuous intracranial pressure (ICP) monitoring was used to assess 46 children and adolescents in whom a clinical diagnosis of arrested hydrocephalus had been made. Thirty patients (Group A) had previously been treated with cerebrospinal fluid diversion and 16 patients (Group B) had no prior treatment of their hydrocephalus. All patients in Group A either had a confirmed nonfunctioning shunt or had undergone shunt removal. Continuous ICP monitoring showed that 80% of the patients in Group A and 63% of those in Group B had episodic or persistent intracranial hypertension. In four patients (25%) whose initial ICP had been normal or equivocal, repeat ICP monitoring later revealed decompensation or reversal of arrest. When serial psychometric testing demonstrated a fall in cognitive functioning, ICP monitoring revealed abnormal ICP's in 88% of patients. This study shows that many patients with apparent arrest of hydrocephalus in fact have an insidiously progressive disorder. Monitoring of ICP and serial psychometric evaluation are therefore valuable tools in the continuing assessment of arrested hydrocephalus.