Fluctuations in sodium levels (SL) can indicate disease severity and independently affect prognosis in critically ill patients. Our primary objective is to study the impact of sodium on clinical outcomes in patients with traumatic brain injury (TBI). This is a single-center, retrospective study of patients with severe TBI from January 1, 2020, to December 31, 2023, inclusive. We found multiple significant relationships between SL and various prognostic factors and outcomes. Statistically significant negative correlations were identified between age and admission SL as well as ICU admission SL (p = 8.79 x10^-8 p = 0.000205). There was a positive correlation with intensive care unit (ICU) discharge levels (p = 0.0301) and no significance for hospital discharge or death. Differences in SL upon admission were statistically significant across four age ranges (pediatric, young adult, older adults, and elderly) (p = 2.394e-06). ICU admission (p = 0.00633), hospital discharge (p = 0.0266), and death (p = 0.0413) also showed significance. We compared sodium ranges (extreme hyponatremia, hyponatremia, normonatremia, hypernatremia, and extreme hypernatremia) and found statistically significant differences in SL at admission, ICU admission, and ICU discharge when compared to admission injury severity scores and Glasgow Coma Scale (GCS) scores. A linear regression analysis revealed a statistically significant positive correlation between ICU admission SL and ISS. We discovered statistically significant differences when comparing ICU admission levels to hospital length of stay (LOS), ventilator days, and mortality. Additionally, we noted positive correlations between ICU admission SL and several factors, including hospital LOS, ICU LOS, ventilator days, and mortality. Finally, the variation in SL from hospital admission to ICU admission was positively correlated with hospital LOS (p = 0.0148), ventilator days (p = 0.0261), and mortality (p=6.9x10^-8). Our findings show that hypernatremia is linked to poorer outcomes in patients with TBI, providing useful clinical insight into the management of critically ill patients with TBI. Further studies examining other metabolites would be beneficial for gaining a deeper understanding of the complex pathophysiology of TBI.