Hyponatremia is a common finding after subarachnoid hemorrhaging (SAH) and can be caused by either cerebral salt-wasting syndrome (CSWS) or syndrome of inappropriate antidiuretic hormone (SIADH). Distinguishing between these two entities can be difficult because they have similar manifestations, including hyponatremia, serum hypo-osmolality, and high urine osmolality. We herein report the case of a 60-year-old man who suffered from SAH complicated by hyponatremia. During his initial hospitalization, he was diagnosed with CSWS. He was readmitted one week later with hyponatremia and was diagnosed with SIADH. This is the first report of SAH causing CSWS followed by SIADH. These two different sources of hyponatremia require different treatments.