The authors report the three principal characteristics of hemispheric ischaemic attacks on CT scan and their development over time: hypodensity, mass effect and contrast enhancement. Their pathophysiological mechanism and prognostic importance are discussed. The topography of the territories of the large arteries vascularising the brain and their main branches is described on the basis of twelve sections cut parallel to the cantho-meatal line. Finally, selected special aspects are described (misleading aspects, haemorrhagic infarcts, border zone infarcts).