We report a 10-year-old boy with chronic enteroviral meningitis associated with agammaglobulinemia (CEMA) and hydrocephalus. He was treated with a low-dose intravenous administration (100 mg/kg/4 weeks) of gammaglobulin (gamma-gl) since he was diagnosed as having Bruton type agammaglobulinemia at 1 year of age. At this admission, neurological examination revealed meningeal signs, Babinski sign, frontal signs, urinary incontinence, and mental retardation (IQ = 48) which was considered to be a sequela of the enteroviral encephalitis which had occurred in his first year of life. T 1-weighted MR imaging of the brain following gadolinium administration revealed a marked dilatation of the lateral ventricles and dense enhancement of the meninges. Enterovirus was detected in the cerebrospinal fluid (CSF) using tissue culture. Histological examination of a biopsied leptomeningeal specimen revealed inflammatory thickening, which was a likely cause of the obstruction to the flow of CSF. The hydrocephalus in this patient was treated with external drainage of CSF from the lateral ventricle. The CEMA was brought into remission by means of the intraventricular administration of gamma-gl, at a dose of 125-250 mg/week (total dose: 1.5 g/8 weeks), in addition to the high dose intravenous administration (400 mg/kg/4 weeks) of gamma-gl. Because of the poor prognosis of patients with CEMA, the intraventricular administration of gamma-gl should be initiated immediately following a diagnosis of enteroviral meningitis.