Background <p>Hyponatremia is common in critically ill children, and may be triggered by trauma-related stress responses. However, its clinical impact in pediatric trauma remains poorly defined. In this study, we investigated the incidence, risk factors, and outcomes of hyponatremia in pediatric patients with trauma.</p> Methods <p>This retrospective observational study investigated patients younger than 19 years admitted to a level I trauma center between 2016 and 2024 who had at least two serum sodium measurements during hospitalization. Patient demographic/anthropometric characteristics and trauma-related data were retrieved. Subsequently, demographic and admission/resuscitation characteristics were compared between patients with and without hyponatremia to investigate the epidemiology and risk factors of hyponatremia.</p> Results <p>Of 469 patients, 166 (35.4%) developed hyponatremia. In multivariable logistic regression analysis, very severe injury (ISS ≥ 25), surgical intervention, and early transfusion were identified as independent risk factors for hyponatremia. After adjustment for confounding variables, hyponatremia was independently associated with longer hospital stay, prolonged ICU stay, and increased duration of mechanical ventilation.</p> Conclusions <p>Hyponatremia affects over one-third of pediatric patients with trauma and is strongly associated with injury severity and increased resource utilization. Early recognition of hyponatremia may help identify high-risk pediatric trauma patients and support optimized supportive care.</p>