Cerebral salt-wasting syndrome is a disorder in which excessive natriuresis and subsequent hyponatremic dehydration occur in patients with intracranial diseases. Cerebral salt-wasting syndrome often develops in patients with severe neurosurgical disorders, such as hydrocephalus, cerebral infarction, and tuberculous meningitis. Here, we report on the case of an 8-year-old boy with cerebral salt-wasting syndrome associated with aseptic meningitis. He showed mild developmental retardation and had a history of convulsion. Four days after his admission, cerebral salt-wasting syndrome abruptly started: natriuresis and hyponatremia gradually improved over 10 days. To the best of our knowledge, this is the first report on cerebral salt-wasting syndrome associated with clinically benign aseptic meningitis.