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BACKGROUND Dysnatremias are common and carry a risk of poor prognosis in acute subarachnoid hemorrhage (SAH) patients. The aim of this study was to determine the frequency and outcome of dysnatremias in 344 SAH patients treated by a targeted sodium management regimen. METHODS We performed a 10-year observational dysnatremia study. Hyponatremia was defined as serum sodium (SNa) below 135 mmol/L, hypernatremia SNa above 150 mmol/L. RESULTS Dysnatremia occurred in 35.8% patients; this was more frequently hyponatremia (19.8%) with a mean SNa 132.23±2.09 mmol/L, (16.0% mild, 3.2% moderate, 0.6% severe). Hypernatremia occurred less commonly in 11.9%, P<0.001 with a mean SNa 154.21±3.72 mmol/L, (6.1% mild, 2.9% moderate, 2.9% severe). In 4.8% of patients there were episodes of both dysnatremias. The incidence of hypo-osmolar hyponatremia was 6.4%, Cerebral salt wasting (CSW) 3.5%, syndrome of inappropriate secretion of antidiuretic hormone (SIADH) 0.3% and Central diabetes insipidus 1.7%. The hypernatremic patients had a higher inpatient mortality rate (P=0.001) and a worse overall outcome (P<0.001) than those hyponatremic or normotremic patients. Multivariate logistic regression showed that hypernatremia was an independent risk factor for increased inpatient mortality and poor outcome in patients with SAH. CONCLUSIONS Our 10-year targeted sodium management regimen in acute SAH patients showed that dysnatremias were frequent, predominantly hyponatremia of which the more usual causes were CSW and not SIADH. Hypernatremia was shown to be an independent risk factor for inpatient mortality and poor outcome.