The introduction of brain imaging with computed tomography revolutionised the treatment of patients with acute ischaemic stroke. With the visual differentiation of haemorrhagic stroke from ischaemic stroke, thrombolytic therapy became feasible. The Alberta Stroke Program Early CT Score was devised to quantify the extent of early ischaemic changes in the middle cerebral artery territory on noncontrast computed tomography. With its systematic approach, the score is simple and reliable. However, the assessment of early ischaemic changes and Alberta Stroke Program Early CT scoring require training. The Alberta Stroke Program Early CT Score is a strong predictor of functional outcome. Furthermore, the effectiveness of intraarterial thrombolysis in patients with middle cerebral artery occlusion shows effect modification by the Alberta Stroke Program Early CT Score. This review summarises the Alberta Stroke Program Early CT Score methodology. We illustrate current knowledge regarding Alberta Stroke Program Early CT Score applied to clinical trials and comment on how Alberta Stroke Program Early CT Score may facilitate clinical treatment decision making and future trial design. Moreover, we introduce a modification of the Alberta Stroke Program Early CT Score methodology that disregards isolated cortical swelling, i.e. focal brain swelling without associated parenchymal hypoattenuation, as early ischaemic changes in the Alberta Stroke Program Early CT Score system.