Ischaemic stroke is a treatable medical emergency. In an era of time-dependent reperfusion techniques, it is crucial that an accurate and prompt diagnosis is made. Approximately 30% of patients admitted to hyperacute stroke units are subsequently found not to have a final diagnosis of acute stroke although some of these patients do have incidental or previously symptomatic cerebrovascular disease. These patients do not benefit from thrombolysis and may require the input of other specialists or treatments. Meanwhile, a proportion of patients with acute stroke have unusual presentations and are sometimes initially admitted to general medical admissions units prior to accessing stroke unit care. It is important that atypical presentations of stroke are recognised so that patients are not denied the benefits of stroke unit care and secondary prevention. This article describes some characteristics of common stroke mimics and chameleons, considers how to avoid diagnostic mistakes and discusses the contributory role of imaging.