A symptomatic arachnoid cyst in an elderly patient is rare. We report two cases of symptomatic arachnoid cysts in elderly patients. The first case is that of a 73-year-old woman complaining of headache and speech disturbance. She had an arachnoid cyst in the left interhemispheric fissure. This is rare. Only two interhemispheric arachnoid cysts in the elderly have ever been reported. The other case is that of a 64-year-old woman, having right hemiparesis and dementia and a cyst is shown in her left temporal lobe. Both patients underwent a cystectomy which resulted in the disappearance of their symptoms. Only 56 cases of symptomatic arachnoid cyst over the age of 60 years have ever been reported. We made an analysis of 58 cases, including our two cases, and compared it with child cases. In cases of the elderly, the symptoms are usually headache, hemiparesis, gait disturbance and dementia, which are similar to symptoms of chronic subdural hematoma and normal pressure hydrocephalus. On the other hand, child cases usually reveal signs of intracranial hypertension. Several authors have reported their therapeutic method for child symptomatic arachnoid cysts. However, it is difficult to determine the best method for treating child cases at this time. We think a cystectomy is the first choice of operative procedure for symptomatic arachnoid cyst in the elderly.