Background Traumatic brain injury on its own results in significant mortality and morbidity but it also contributes to complications that manifest as dysnatremia in the majority of cases. Objective The objective of this study is to assess the association of hyponatremia and hypernatremia with the severity of traumatic brain injury and its impact on mortality. Method This is a retrospective, descriptive, and analytic study conducted during a 1-year period from March 2018 to March 2019. The study population was selected from the patients presenting to the emergency department with TBI in the Upendra Devkota Memorial National Institute of Neurological and Allied Sciences, Bansbari, Kathmandu, Nepal. All the patients that fulfilled the inclusion criteria of age were enrolled in the study. Patients with known renal disease due to the higher incidence of electrolyte disbalance were excluded. Association of outcome with hyponatremia and hypernatremia were sought using chi-square, fisher exact test and independent t test using SPSS ver 20. Result Over a period of 1 year, 367 patients with traumatic brain injuries were treated in our hospital. Hyponatremia was seen among 55 patients (14.9%) and hypernatremia was seen among 22 patients (5.99%). The age range of patients included in the study was 16 to 87 with a mean age of 37.96 ± 16.512 years. The male to female ratio was calculated as 3.2:1. Mild, moderate, and severe head injuries were 286 (77.9%), 37 (10.1%), and 44 (12%) respectively. Surgical intervention was performed among 77(21%) individuals. Our series showed an association between the severity of traumatic brain injury and hyponatremia however didn't show an association between the severity of traumatic brain injury and the development of hypernatremia. Conclusion We concluded that the severity of head injury is associated with severity of hyponatremia but not with severity of hypernatremia. Similarly, a strong association existed between the severity of hypernatremia and outcome of patients. However, such association was not seen with hyponatremia.