The authors report the case of a 29-year-old female who presented with symptoms of shunt dysfunction 11 years after first being shunted for an aqueductal stenosis. After numerous revisions she developed an isolated third ventricle, necessitating triventricular shunting to obtain a new equilibrium. An isolated third ventricle is a very rare phenomenon, usually seen in very complex hydrocephalus and only reported on twice before (Filler et al., 1995). Etiological factors postulated in the development of an isolated lateral or fourth ventricle, all seem to contribute also to the development of an isolated third ventricle.