Objectives: Hyponatremia is prevalent electrolyte disorder and can be fatal in older adults. Evaluative studies on hyponatremia among older adults are scarce, especially targeting for those who visited emergency department (ED). We aimed to estimate the prevalence and to identify risk factors of hyponatremia among elderly patients visiting the ED. Methods: A retrospective chart review was completed including 65 or older patients who visited ED at Seoul National University Bundang Hospital from September to December 2019. Patients with the serum sodium concentration of less than 130mEq/L was defined as a hyponatremia group. Logistic regression analysis was conducted to assess predictive factors for hyponatremia. Results: Of the total 2,445 patients, 155 (6.3%) were confirmed to have hyponatremia at the time of ED visits. Risk factors for hyponatremia identified in logistic regression analysis were thiazides (aOR=2.64, 95% CI 1.66-4.21), opioids (exclude tramadol) (aOR=3.45, 95% CI 1.72-6.94), and desmopressin (aOR=6.98, 95% CI 2.45-19.84). Compared to the use of thiazides alone, it was confirmed that the possibility of hyponatremia was more than quadrupled when proton pump inhibitor (PPI) was used together (aOR=4.08, 95% CI 1.74-9.55). Conclusions About 6.3% of older adults visiting the ED had hyponatremia. Age, number of medications taken, previous history of hyponatremia, heart failure, cirrhosis, pneumonia, sepsis, prescribed drugs including thiazides, opioids (exclude tramadol), or desmopressin or taking PPI together with thiazides was confirmed to correlate with the risk of hyponatremia.