Transcranial Doppler ultrasonography is an extremely useful adjunct in neurosurgical intensive care. Continuous improvements in TCD equipment as well as computer software have improved examination success and also vessel identification. Recent expanding applications of TCD have also allowed the study of disorders of control of the cerebral circulation. TCD can be used to detect vessel narrowing from a variety of causes, including vasospasm, and also can be used to detect cerebral emboli and to evaluate CO2 reactivity, autoregulation, and the response to certain medications, as well as to indicate progressive obstruction of the cerebral circulation as seen in conditions leading to brain death. In the future, TCD may offer the ability to estimate the ICP using noninvasive means by evaluating velocity in the middle cerebral artery and arterial blood pressure tracings. The noninvasive determination of cerebral autoregulation may be useful in evaluating strategies to improve cerebral autoregulation as well as aid in the optimal management of ICP control and preservation of optimal cerebral circulation.