Brain imaging is necessary to assess the exact diagnosis and the acute pathophysiological state of the brain. This chapter explores the questions of what unenhanced computed tomography (CT) is able to assess in patients with acute stroke, how accurate this information is, and whether imaging with CT has any impact on stroke diagnosis, stroke treatment and, finally, on the clinical outcome of patients. CT has the capacity to identify different pathophysiological states that results in the same clinical picture of an acute stroke syndrome: intracranial hemorrhage, ischemic edema and ischemia without ischemic edema. Surgery or autopsy regularly confirms the CT finding of intracranial hemorrhage. CT was the first imaging modality that could reliably differentiate between hemorrhagic and ischemic stroke. MRI was introduced into clinical practice as the second modality that can image brain parenchyma, and is now considered as an evolving standard of care in acute stroke.