Introduction: Hyponatremia (HN) is the most common electrolyte disorder, and is documented in 15-30% of hospitalized patients. However, 30-40% of ICU patients have HN, and these patients have high mortality rates. Because few studies have been published in the ICU population, this is the first registry to evaluate demographics and current practice patterns, and to assess outcomes such as length of stay in ICU patients. Hypothesis: There is variability in the management of HN in ICU patients Methods: This is a multicenter, multinational, observational registry of hyponatremic adults with euvolemia (SIADH) and hypervolemia (cirrhosis, HF, and nephrotic syndrome). HN is defined as serum sodium concentration ([Na+]) <130mmol/L, and overcorrection as > 12 mmol/L change in 24h. Target enrollment is 5,000 patients globally. After informed consent or waiver, medical records of eligible patients were abstracted and summarized using descriptive statistics Results: A total of 664 ICU patients in the US, out of 2377, were analyzed through August 2012. The mean entry and discharge [Na+] were 126.6 ± 10.0 mmol/L, and 132.6 ± 5.5mmol/L, respectively. HN etiology was heart failure (HF) in (44%), SIADH (33%), cirrhosis (16%), and nephrotic syndrome (4%). HN was the admitting diagnosis in 20%, and was chronic in 34%. A total of 32% remained hyponatremic at discharge, most commonly in patients treated with fluid restriction (FR) alone. Overall, 24% of patients received no treatment, and monotherapy with FR (20%), normal saline (NS) (11%), any pharmacologic therapy(3%), or hypertonic saline (3%). Combination therapy was initially prescribed in 18%. Overcorrection of [Na+] developed in 2% overall, 17% receiving hypertonic saline only, 9% receiving NS only, 2% no therapy, and in no patient received FR only or vasopressor receptor antagonist only. Conclusions: ICU patients are often admitted with chronic HN and frequently have SIADH or HF. One fourth of patients received no treatment for HN, with FR the most common monotherapy. Overcorrection most commonly occurred in patients receiving hypertonic saline. Patients are frequently discharged with HN. These data suggest HN in ICU patients is managed inconsistently and often suboptimally.