Isolated fourth(IV) ventricle in shunted patients has been reported with increasing frequency. Symptomatic isolated IV ventricular hydrocephalus in adults, however, has seldom been described. We report five such cases among total of 420 shunted cases in our institution from January 1992 to December 1995. The causes of initial hydrocephalus were postsurgical meningitis(SAH, teratoma and abscess of posterior fossa), tuberculous meningitis and neurocysticercosis of the IV ventricle. All cases were symptomatic with clinical findings related to posterior fossa lesions. Two patients developd symptoms in 2 months after V-P shunts and the others between 17 and 118 months after V-P shunts. These 5 patients required IV ventricular shunting. All patients improve postoperatively except one patient who developed 6th nerve palsy related to secondary irritation of the brainstem by the IV ventricular catheter. Inflammatory changes in the ependyma of both aqueduct of Sylvius, foramina Luschka and Magendi have been regarded as the most important factors in the development of the isolation of IV ventricle, especially in adults. It is generally recommended to shunt in cases of the adult symptomatic isolated IV ventricle. Alternative surgical techniques and prevention of such complications are discussed.