Subependymomas are benign neoplasms, accounting for 0.5 % of all central nervous system tumors. These tumors are frequently asymptomatic, often discovered incidentally at autopsy. However, patients may be symptomatic with the symptoms depending on location of the tumor. Since subependymomas typically arise from the ventricular wall, obstruction of cerebrospinal fluid is a major cause of onset symptoms. We present a rare case report of a subependymoma at the foramen of Monro presenting with intermittent hydrocephalus. The patient's tumor was asymptomatic for many years. Imaging findings included asymmetry of the lateral ventricles. The patient developed sudden onset of headache and altered mental status followed by complete resolution, likely due to intermittent hydrocephalus. She developed two more such episodes necessitating an emergent external ventricular drain placement followed by surgical resection. Our report illustrates a case of intermittent hydrocephalus due to a sessile subependymoma. Even though our patient presented with a histologically benign ventricular tumor, she demonstrated rapidly worsening symptoms that culminated in herniation. By presenting our case report, we hope to draw attention to this rare but potentially life-threatening presentation of subependymoma. Once diagnosed, we recommend early tumor removal and restoration of normal cerebrospinal fluid (CSF) pathways for these intraventricular tumors.