The authors report on a patient harbouring an unruptured cortical arteriovenous malformation (AVM), who had presented with obstructive hydrocephalus due to compression of the cerebral aqueduct by a large venous varix. A ventriculoperitoneal (VP) shunt was inserted in emergency. Due to its large volume, the AVM was not referred for treatment and a follow-up policy was chosen. After the second VP shunt dysfunction, endoscopic third ventriculostomy was performed under neuronavigation. The procedure went uneventfully and the patient recovered well. In the rare eventuality of obstructive hydrocephalous caused by an unruptured AVM, endoscopic third ventriculostomy is feasible, efficient and can avoid shunt-related complications.