Transcranial Doppler (TCD) is increasingly utilized in patients with lifethreatening neurologic injury and has several practical applications in neurocritical care. It holds promise for the diagnosis and monitoring of vasospasm (VSP) in patients with subarachnoid hemorrhage (SAH) and the detection of increased intracranial hypertension. In addition, it has the ability to estimate flow velocity alterations, associated with critical decrease in cerebral perfusion pressure, in patients with clinical diagnosis of brain death (BD). It is easily performed, it is relatively inexpensive and non invasive and can aid intensivists in optimizing neurovascular dynamics for the individual patient. In general, TCD findings in different clinical scenarios can be useful tools for screening neurocritical patients during clinical trials for the development of new therapeutic treatments, leading to improvement in final outcome. In this article we will try to describe basic technical issues regarding TCD instrument and examination and we will also try to provide a description of indications and findings in patients with subarachnoid hemorrhage and brain death clinical diagnosis, through the presentation of a case report with SAH and subsequent vasospasm leading to BD, treated in the Intensive Care Unit of a University Hospital.