A 44-year-old woman presented with a rare case of disproportionately large communicating fourth ventricle (DLCFV) associated with syringomyelia and intradural arachnoid cyst in the spinal cord. Ventriculoperitoneal shunt operation was performed for hydrocephalus after subarachnoid hemorrhage. She developed DLCFV, which was then associated with syringomyelia and spinal intradural arachnoid cyst. Shunting of the fourth ventricle improved DLCFV, and then the syringomyelia and arachnoid cyst. Although the aqueduct was patent, independent pressure control of the fourth ventricle and the other ventricles was necessary to improve the symptoms. Shunting of the fourth ventricle should be considered for patients with DLCFV when the symptoms persist despite adequate pressure control of the other ventricles.