Transcranial Doppler sonography (TCD) is a non-invasive method that can be repeated to measure blood flow velocity in intracranial arteries and to assess cerebrovascular reactivity in patients with a variety of neurological diseases. The aim of this study was Doppler sonography evaluation of blood flow and reactivity in the middle cerebral artery in patients at different stages after mild head injuries. The dynamic assessment of blood flow velocity and pulsatility index both at rest and after hyperventilation in 73 patients with mild head injuries was carried out on the day of injury, the third day, sixth day and after 6 months to 5 years. The control group consisted of 61 healthy volunteers. Obtained results indicate an increase in blood flow velocity in the middle cerebral artery on the day of injury and a decrease within the following days in younger patients (aged xleq 30 yrs). Also their cerebrovascular reactivity was significantly lower. In older persons (age > 30 yrs) and in patients with remotely suffered injuries, neither blood flow velocity in the middle cerebral arteries nor cerebrovascular reactivity differed significantly from the results of the respective age control groups. The findings justify a conclusion that mild head injury is followed by changes both in the blood flow and cerebrovascular reactivity. In younger patients with mild head injuries these haemodynamic disturbances seem to be connected with altered activity of the autonomic system.