Elevated blood flow velocity (BFV), measured by transcranial Doppler (TCD), has been associated with hyperemia and cerebral vasospasm. This study examined whether the lack of a diastolic notch within the TCD waveform was associated with relative hyperemia within 5 days after injury in 35 traumatic brain injured (TBI) patients. Hyperemia (avDO2of < 4 ml/dL) was present in 16 patients and absent in 19 patients. Two clinicians independently coded TCD waveforms based on the presence of a diastolic notch (88% agreement). There was no significant difference in the presence of a diastolic notch by group; a diastolic notch was present in 57% (11/19) of patients without hyperemia and 81% (13/16) of patients with hyperemia. Sensitivity and specificity of detecting hyperemia using the diastolic notch was 18.7% and 57.9% respectively. The results showed that relative hyperemia was present without an elevation in blood flow velocities, and that the lack of a diastolic notch did not detect the presence of hyperemia in the TBI patient.