In recent years transcranial Doppler and duplex sonography have become valuable methods supplementary to extracranial vascular investigations and especially in intensive care medicine. High grade stenoses and occlusions of the basal cerebral arteries as well as vascular spasms after subarachnoidal haemorrhage can be assessed using well-known Doppler criteria. Since it can reliably detect significantly enhanced intracranial pressure, the Doppler technique can be used also for shortening the waiting time in confirming brain death. The patency of the intracranial collateral pathways can be estimated qualitatively, and the CO2 and Diamox test enables quantitative evaluation of cerebral haemodynamics. Moreover, in future, detecting spontaneous and contrast media-induced intracranial emboli may contribute to the differentiation of cerebral ischaemic events.