Background: Hyponatremia is observed in children with meningitis, encephalitis, pneumonia, urinary tract infections, and Kawasaki disease. The presence of hyponatremia is associated with increased morbidity and mortality in adults. The clinical significance of hyponatremia in febrile pediatric patients is unknown. The objective of this study was to evaluate the prevalence and prognostic value of hyponatremia in children presenting to the emergency department (ED) with systemic inflammatory response syndrome (SIRS). Methods: This retrospective study included children 1-19 years-old presenting to the ED between January-December 2014 with fever and SIRS. Exclusion criteria included comorbidities affecting sodium levels such as diuretic use, renal insufficiency, hyperglycemia, or immune deficiencies. Hyponatremia was defined as serum sodium of < 132 mEq/L; the primary outcome was hospital admission. Continuous non-normal variables were described as median and interquartile range. Categorical variables were compared using Chi-squared or Fisher's Exact Tests. Spearman correlation was evaluated between nonparametric variables. Level of significance was set at 0.05. Results: Out of 4,791 patients, 663 met inclusion criteria by having electrolytes collected and by triggering SIRS Best Practice Alerts. Hyponatremia occurred in 19%. Patients with hyponatremia were older (P = 0.04) and had higher maximum body temperature (P < 0.001), white blood cell counts (P = 0.04), and C-reactive protein levels (P = 0.004). Patients with hyponatremia also had higher rates of admission (P = 0.003, OR = 1.9, 95% CI [1.3-2.9]) and bacteremia (P = 0.009). Conclusions: Hyponatremia is often found among pediatric patients presenting to the ED with febrile SIRS and is associated with increased morbidity.