Ultrasound Doppler sonography with miniaturized probes and high resolution offers new possibilities of intraoperative control of neurovascular procedures. Patency, flow direction stenoses and changes in resistance can be investigated atraumatically, repeatedly and without additional preparation. In bypass and aneurysm surgery, about 10% of the cases were shown by Doppler examinations to be unsatisfactory, with stenoses and occlusions. These could be immediately corrected without loss of time. In normal cases, the information on the local haemodynamics enlarges the knowledge as to the effects of the operation and make it safer. Real time ultrasonography, which can be easily adapted to neurosurgery, is a new atraumatic tool for localizing, in two dimensions, subcortical intrinsic processes, haematomas, ventricles ect. It is useful for guided biopsies and punctures and for the centering of the dura and brain incision over the middle of the lesion, especially in microsurgical procedures.