#### The bottom line Stroke is increasingly common and often fatal or disabling.1 The absence of a definitive diagnostic test for stroke and the potential for emergency interventions to restore brain perfusion,2 improve survival free of handicap, and minimise early recurrent stroke3 mean that doctors need to be able to diagnose acute stroke rapidly and accurately. Stroke is not consistently defined in clinical practice, clinical research, and public health. Traditionally, stroke has been defined clinically by the abrupt onset of symptoms of focal neurological dysfunction that last more than 24 hours (or lead to earlier death) and are caused by acute vascular injury to part of the brain.4 The vascular causes include inadequate blood supply to part of the brain or spinal cord (ischaemic stroke, arterial or venous) and spontaneous haemorrhage into part of the brain (primary intracerebral haemorrhage) or over …