Although cognitive impairment is one of the major symptoms of ventricular tumors, few studies have reported the details of cognitive impairment before and after their surgical removal. The expected effects on cognitive function should also be considered when choosing a surgical approach. We report the case of a large lateral ventricle meningioma in which cognitive impairment was detected on detailed neuropsychological examinations. The tumor was totally removed through the right superior temporal gyrus. Postoperative neuropsychological assessment revealed the reversal of cognitive impairment. As cognitive impairment is complex and easily overlooked, it is important to precisely assess neuropsychological function in patients with large brain tumors.