Computed tomography (CT) is widely used for early evaluation of acute strokes. Most importantly, CT excludes acute hemorrhage or other diseases mimicking ischemia. Therefore, CT is the main imaging examination in patients with brain ischemia and when antithrombotic agents are being considered. During the first hours after acute ischemic stroke, the CT does not usually show much in the first 24 hours. However, early abnormal findings on CT scan have been described such as the hyperdense middle cerebral artery sign (HMCAS), and reduced contrast attenuation of the cerebral parenchyma. HMCAS reflects arterial occlusion. Early parenchymal abnormalities, the attenuation of lentiform nucleus (ALN), loss of the insular ribbon (LIR) or hemispheric sulcus effacement (HSE) occur less frequently and they are positive criteria for cerebral in progress. Early parenchymal abnormalities might also predict subsequent infarct extension and hemorrhagic transformation. Therapeutic trials of ischemia in MCA territory involved decision making when the CT may not show obvious ischemic changes. Finally, initial CT findings may also help to predict response to therapy.