OBJECTIVES: Hyponatremia (HN) is the leading electrolyte abnormality among hospitalized patients. In the absence of symptoms, HN is often overlooked as a condition that warrants aggressive intervention. Though HN is common, little is known regarding the influence of HN on patient outcomes and healthcare resource utilization. This study assessed the impact of HN on inpatient total and intensive care unit (ICU) cost, total and ICU length of stay (LOS), likelihood of ICU admission, and 30-, 90-, and 180-day readmission.  METHODS: Premier’s Perspective® database was utilized to construct a stratified sample of hospital inpatients discharged between January 1, 2007 and June 30, 2009. HN patients were identified using primary or secondary diagnosis of HN (n=558,815) and were matched to a non-HN control group (n=558,815) using exact matching of age, gender, provider region, and 3M™ APR-DRG assignment. Matching was further refined using propensity scores based on additional patient and hospital characteristics and patient comorbidities. Cost was analyzed using a multivariate general linear regression model with gamma distribution and log-link, LOS with negative binomial distribution and log-link, and ICU admission and hospital readmission with multivariate logistic regression.  RESULTS: In contrast to non-HN patients, patients with HN had significantly higher total inpatient cost (9.49%, CI=8.99-10.00; p<.0001), ICU cost (9.12%; CI=8.04-10.23; p<.0001), total LOS (12.24%, CI=11.85-12.64; p<.0001), and ICU LOS (11.06%, CI=9.60-12.54; p<.0001). HN patients were significantly more likely to be admitted to the ICU (OR=1.027, CI=1.016-1.037; p<.0001), and readmitted at 30 (OR=1.129, CI=1.118-1.141; p<.0001), 90 (OR=1.185, CI=1.175-1.196; p<.0001), and 180 (OR=1.163, CI= 1.153-1.173; p<.0001) days post discharge compared to non-HN patients.  CONCLUSIONS: HN represents a significant clinical, utilization, and economic burden due to increased cost, LOS, ICU admissions and hospital readmission