Many studies have indicated that hypernatremia is associated with increased mortality. In this study, we aimed to explore the relationship between intensive care unit (ICU)-acquired hypernatremia and the prognosis of critically neurological patients.Based on serum sodium level in the ICU, 450 patients were divided into 3 groups: 222 had normal serum sodium, 142 had mild hypernatremia, and 86 had severe hypernatremia. Kaplan–Meier and multivariable binary logistic regression analyses were performed to evaluate the prognostic value of hypernatremia in critically neurological patients. Receiver operating characteristic (ROC) curve was constructed for serum sodium levels to determine their roles in predicting ICU mortality.Hypernatremia was significantly related with age, Glasgow Coma Scale (GCS) score, serum sodium, APACHE II score, and serum creatinine. Moreover, the different treatment outcome including mechanical ventilation, the days of stayed in ICU, and Glasgow Outcome Scale score had correlation with serum sodium levels. Old ages, GCS score, therapeutic intervention scoring system (TISS) score, APACHE II score, serum sodium peak, and so on were all associated with the mortality. In addition, hypernatremia was an independent prognostic factor for critically neurological patients by logistic regression analysis (odds ratio = 1.192, 95% confidence interval = 1.135–1.252, P = 0.000). Moreover, we got the sensitivity of 79.4% and specificity of 74.5% in the ROC analysis between peak serum sodium and the mortality. The area under the ROC curve was 0.844, and the optimal cutoff value was 147.55.Our results showed that ICU-acquired hypernatremia may be a potential prognosis marker for critically neurological patients.