Methods The COBI (Continuous hyperosmolar therapy in traumatic brain-injured patients) trial is a multicenter, randomized, controlled, open-label, two-arms study with blinded adjudication of primary outcome. Three hundred and seventy patients hospitalized in Intensive Care Unit with a traumatic brain injury (Glasgow Coma Scale ≤ 12 and abnormal brain CT-scan) are randomized in the first 24 hours following trauma to standard care or continuous hyperosmolar therapy (NaCl 20%) plus standard care. Continuous hyperosmolar therapy is maintained for at least 48 hours in the treatment group and continued for as long as is necessary to prevent intracranial hypertension. The primary outcome is the score on the Extended Glasgow Outcome Scale (GOS-E) at 6 months. The treatment effect is estimated with ordinal logistic regression adjusted for pre-specified prognostic factors and expressed as a common odds ratio.