Perfusion computed tomography is a relatively new technique that allows rapid qualitative and quantitative evaluation of cerebral perfusion by generating maps of cerebral blood flow (CBF), cerebral blood volume (CBV) and mean transit time (MTT). The technique is based on the central volume principle: CBF=CBV/MTT. Perfusion CT has been found to be useful for noninvasive diagnosis of cerebral ischemia and infarction, for the evaluation of vasospasm after subarachnoid hemorrhage, for defining abnormal regions of blood pool in brain tumors. Perfusion CT in patients with severe head trauma provides independent prognostic information regarding functional outcome. The technique is widely available at low cost, accurate and easy to perform. This article is a review of the technique, clinical applications, and controversies surrounding perfusion CT.