We report a case of non communicating hydrocephalus due to membranous obstruction of Magendie's foramen. A 37-year-old woman presented with intracranial hypertension symptoms caused by the occlusion of Magendie's foramen by a membrane probably due to arachnoiditis. As far as the patient's past medical history is concerned, an Epstein-Barr virus infectious mononucleosis was described. Fundoscopic examination revealed bilateral papilledema. Brain magnetic resonance imaging demonstrated a significant ventricular dilatation of all ventricles and turbulent flow of cerebelospinal fluid (CSF) in the fourth ventricle as well as back flow of CSF through the Monro's foramen to the lateral ventricles. The patient underwent a suboccipital craniotomy with C1 laminectomy. An occlusion of Magendie's foramen by a thickened membrane was recognized and it was incised and removed. We confirm the existence of hydrocephalus caused by fourth ventricle outflow obstruction by a membrane. The nature of this rare entity is difficult to demonstrate because of the complex morphology of the fourth ventricle. Treatment with surgical exploration and incision of the thickened membrane proved to be a reliable method of treatment without the necessity of endoscopic third ventriculostomy or catheter placement.