Early neurological deterioration is common after acute stroke and is associated with increased disability and mortality. There are a number of mechanisms involved with neurological deterioration which can be divided into firstly, neurological causes as a result of the direct consequence of the neurological insult to the brain, and secondly, non-neurological causes such as abnormal physiological parameters. Both of these mechanisms can lead to secondary neuronal damage within the ischaemic penumbra. Many of these factors are potentially reversible, and therefore it is crucial that appropriate monitoring is undertaken to identify high risk patients.