In a retrospective review of all cases with a diagnosis of idiopathic intracranial hypertension in two academic departments of neurology over a nine-year period, the authors identified six patients with a clinical course typical of idiopathic intracranial hypertension (IIH) except for the finding of cerebrospinal fluid pleocytosis. There were five women and one man with a mean age at presentation of 25.7 years (range, 25-32 yr). All were obese but had no other associated medical conditions or identifiable risk factors for IIH. In five patients, all or most cerebrospinal fluid cells were lymphocytes. Cerebrospinal fluid pleocytosis persisted for several months in all patients. Patients underwent a thorough laboratory and neuroimaging evaluation that did not reveal a primary cause. Medical treatment directed solely at lowering intracranial pressure was effective in five patients; one patient required lumboperitoneal shunting. Ophthalmic manifestations of increased intracranial pressure stabilized or remitted after treatment was withdrawn with a mean follow-up period of 33 months (range, 14-55 mo). Some patients may present with idiopathic chronic meningitis and elevated intracranial pressure that responds to treatment used for IIH.