OBJECTIVE: To investigate the contribution of transcranial Doppler measurements obtained in the emergency room for detecting patients with secondary neurological deterioration after mild or moderate brain trauma. DESIGN AND SETTING: Prospective cohort study in the emergency room in a university teaching hospital. PATIENTS: Seventy-eight adult patients admitted to the emergency room after a traumatic brain injury (TBI), including 42 patients with Glasgow Coma Score 14-15 and 36 with 9-13. MEASUREMENTS AND RESULTS: All patients had transcranial Doppler measurements on both middle cerebral arteries and computed tomography on admission. Neurological outcome was assessed 7 days after trauma. Of the patients included 7 and 10 had secondary neurological deterioration after mild and moderate TBI, respectively. On admission these groups of patients had significantly more injuries on computed tomography using the Trauma Coma Data Bank classification and higher pulsatility index using transcranial Doppler than the patients having no subsequent neurological worsening. CONCLUSIONS: Increased pulsatility index after mild or moderate TBI is a reason for concern about the possibility of further neurological deterioration. Computed tomography and Doppler measurements could be combined to detect on admission patients at risk for secondary neurological deterioration in order to improve their initial disposition.