Background: Hypernatremia is a frequently encountered electrolyte disorders in hospitalized patients. Controversies still exist over the relationship between hypernatremia and its outcomes in hospitalized patients. This study examines the relationship of hypernatremia to outcomes among hospitalized patients and to examine the extent to which this relationship varies by kidney function and age. Methods: We conducted an observational study to investigate the association between hypernatremia, eGFR and age at hospital admission and in-hospital mortality, and discharge dispositions. We analyzed the data of 1.9 million patients extracted from the Cerner Health Facts databases (2000-2018). Adjusted multinomial regression models were used to estimate the relationship of hypernatremia to outcomes of hospitalized patients. Results: Of all hospitalized patients, 3.2% had serum sodium ([Na]) >145 at hospital admission. Incidence of in-hospital mortality was 11.7% and 2.2% in hyper- and normonatremic patients, respectively. The risk of all outcomes increased significantly for [Na] >155 mEq/L compared to the reference interval of [Na]: 135-145 mEq/L. Odds Ratios (95% confidence interval) for in-hospital mortality, discharge to hospice and discharge to nursing facilities were 34.41 (30.59-38.71), 21.14 (17.53-25.50) and 12.21 (10.95-13.61), respectively, (p<0.001, for all). In adjusted models, we found the association between [Na] and disposition was modified by eGFR (p<0.001) and by age (p<0.001). Sensitivity analyses were performed using the eGFR equation without race as a covariate and the inferences did not substantially change. In all hypernatremic groups, patients aged 76-89 and ≥90 had higher odds of in-hospital mortality compared to younger patients (p<0.001, for all). Conclusions: Hypernatremia was significantly associated with in-hospital mortality, discharge to hospice or to nursing facility. The risk of in-hospital mortality and other outcomes was highest among those with [Na]>155 mEq/L. This work demonstrates that hypernatremia is an important factor related to discharge disposition and supports the need to study whether protocolized treatment of hypernatremia improves outcomes.