Isolated fourth ventricle[IFV] is a rare entity producing symptoms of a progressive posterior fossa mass lesion. It is mainly reported in a patient who undergo shunt placement as its late complication. However, its surgical management has been difficult and its optional treatment remains controversial. We had an occasion to admit 19-year-old female to our hospital due to hydrocephalus : she had a history of meningitis when she was 2 years old. Ten years later she was diagnosed as hydrocephalus and managed by lateral ventriculo-peritoneal shunting procedure. Seven years after the procedure, the patient presented with headache, nausea, truncal ataxia and nystagmus. Computed tomography and magnetic resonance image scan demonstrated markedly enlarged fourth ventricle : and thus, neuroendoscopic aqueductoplasty and aqueductal stent insertion was performed. The authors present a case of an IFV after lateral ventriculo-peritoneal shunting for hydrocephalus, which was treated successfully with a neuroendoscopic surgery. The technique of this procedure is described below.