The relation between acute ischaemic stroke and infection is complex. Infection appears to be an important trigger that precedes up to a third of ischaemic strokes and can bring about stroke through a range of potential mechanisms. Infections that present subsequent to stroke also complicate up to a third of cases of stroke and might worsen outcome. Inflammatory responses, which are a defence mechanism against infection but can also be a pathogenic mechanism that precipitates stroke and neurological sequelae, are important features. Although factors such as stroke severity and dysphagia are important predictors of poststroke infection, there is evidence from experimental and clinical settings of impaired immunity or brain-induced immunodepression after stroke. Greater understanding of the relation between inflammation and both infection and ischaemic mechanisms is needed. This might be particularly important because new treatment strategies for acute ischaemic stroke are being investigated, including those that modulate cytokines and the immune system.