CT perfusion images can be rapidly obtained on all modern CT scanners and easily incorporated into an acute stroke imaging protocol. Here we discuss the technique of CT perfusion imaging, how to interpret the data and how it can contribute to the diagnosis of acute stroke and selection of patients for treatment. Many patients with acute stroke are excluded from reperfusion therapy if the onset time is not known or if they present outside of traditional treatment time windows. There is a growing body of evidence supporting the use of perfusion imaging in these patients to identify patterns of brain perfusion that are favourable for recanalisation therapy.