Traumatic brain injury patients are routinely treated with osmotherapy such as mannitol and/or hypertonic saline for reducing the intracranial pressure. We observed that these patients are developing hyponatremia after 3-5 days of being given osmotherapy and this delayed hyponatremia led to prolongation of hospital stay and requirement of additional medications such as Fludrocortisone. We also observed that delayed hyponatremia was seen more commonly in patients treated with hypertonic saline when compared to those treated with mannitol. This has not been reported in literature. Hence, we designed this randomized controlled trial where patients with traumatic brain injury requiring osmotherapy will be randomized to receive either hypertonic saline or mannitol and we will assess the incidence of delayed hyponatremia in both groups and the relative risk as the primary outcome measure. We will also study the secondary outcome measures such as duration of ICU/hospital stay, requirement of Fludrocortisone and/or Prednisolone and need for surgical intervention. This study will help us to assess if the delayed hyponatremia seen in traumatic brain injury patients undergoing osmotherapy can be attributed to the use of hypertonic saline and whether preference to use mannitol instead of hypertonic saline as the first osmotherapeutic agent in traumatic brain injury patients can be justified.