Background: After mild traumatic brain injury (TBI), discharge from the emergency department (ED) relies on clinical examination and brain imaging, but triaging of these patients can be challenging in specific situations. Transcranial Doppler (TCD) after mild TBI may rule out early neurologic worsening. We hypothesize that patients with mild TBI and normal TCD can be safely discharged home immediately after the ED. Methods: This is a prospective, open-label, multisite, randomized controlled noninferiority trial. Eligible patients are mild TBI patients (Glasgow Coma Scale, GCS, 13-15 on admission) with minor lesions on brain CT scan or normal CT scan but one of the following risk factors: (1) GCS = 14 after CT scan; (2) alcoholic intoxication, (3) ongoing treatment with anticoagulants or anti-platelet therapy; (4) persisting nausea, vomiting, and/or headaches; or (5) early initial CT scan (< 4 h after TBI). Patients randomized in the intervention group have TCD within 12 h after TBI and can be immediately discharged from the ED if TCD is normal (diastolic flow velocity higher than 25 cm/s and pulsatility index lower than 1.25). Discharge of patients in the control group relies on clinical examination and brain imaging only. The primary outcome is the 3-month neurological outcome measured with the Extended Glasgow Outcome Scale (GOS-E). Secondary outcomes are the GOS-E at 1 month, the QOLIBRI (Quality of life after TBI) and EQ-5D-5L questionnaires at 1 month and 3 months after TBI, the Rivermead Post-Concussion Symptoms questionnaire at 1 month and 3 months after TBI, mortality within the first 3 months, the number of cerebral CT scans, length of stay in hospital, the number of thromboembolic events or diagnosed nosocomial infections, and the number of patients re-admitted to hospital in relation with the initial TBI. Inclusions have started in February 2020 and are expected to be complete by June 2025. Discussion: Transcranial Doppler in mild TBI patients may help immediate discharge from the ED after CT scanning.