Hyponatremia is a frequent complication following subarachnoid hemorrhage (SAH), and is commonly attributed either to the syndrome of inappropriate antidiuretic hormone secretion (SIADH) or cerebral salt wasting syndrome (CSW). The object of this study is to elucidate the clinical demographics and sequelae of hyponatremia due to CSW in subjects with aneurysmal SAH. Retrospective chart review of patients >18 years with aneurysmal SAH admitted between January 2004 and July 2007 was performed. Subjects with moderate to severe hyponatremia (serum sodium <130 mmol l(-1)) were divided into groups consistent with CSW and SIADH based on urine output, fluid balance, natriuresis, and response to saline infusion. Clinical demographics were compared. Of 316 subjects identified, hyponatremia (serum sodium <135 mmol l(-1)) was detected in 187 (59.2%) subjects and moderate to severe hyponatremia in 48 (15.2%). Of the latter group, 35.4% were categorized with SIADH and 22.9% with CSW. Compared to eunatremic subjects, hyponatremia was associated with significantly longer hospital stay (15.7 +/- 1.9 vs. 9.6 +/- 1.1 days, p < 0.001). Subjects with CSW had similar mortality and duration of hospital stay vs. those with SIADH. Though less common than SIADH, CSW was detected in approximately 23% of patients with history of aneurysmal SAH and was not clearly associated with enhanced morbidity and mortality compared to subjects with SIADH. Further studies regarding the pathogenesis and management, along with the medical consequences, of CSW are important.