Two cases of disproportionately large communicating fourth ventricle (DLCFV) accompanied by consciousness disturbance and bilateral exotropia are reported. Case #1 was a 21-year-old male who suffered from consciousness disturbance and bilateral exotropia due to malfunction of the ventriculoperitoneal shunt (VPS) which had previously been operated on twice for a left parietal arteriovenous malformation, which had caused ventricular hemorrhage several times. The last hemorrhage was massive and made ventricular casting, including the fourth ventricle. Both bilateral exotropia and the fourth ventricular dilatation were well controlled by the reconstruction of the VPS. Case #2 was a 66-year-old female, semicomatous because of massive subarachnoid hemorrhage with ventricular casting hematoma due to rupture of the right middle cerebral aneurysm. Though an improvement of the consciousness disturbance was obtained by continuous ventricular drainage (CVD), bilateral exotropia and consciousness deterioration appeared after lumboperitoneal shunt followed by the removal of the CVD. Another CVD was then carried out and some improvement was obtained again. However, the same symptoms appeared again after the VPS, followed by the removal of the CVD. The patient finally died despite a third CVD. Autopsy revealed a markedly dilated fourth ventricle and massive subarachnoid clots particularly around the foramen of Magendie and Luschka. The pathogenesis of DLCFV and bilateral exotropia are also discussed.