The cerebral collaterals play an important role in penumbral tissue sustenance after an acute ischemic stroke. Recent studies have demonstrated the potential role of collaterals in the selection of acute ischemic stroke patients eligible for reperfusion therapy. However, the understanding of the significance and evidence around the role of collateral status in predicting outcomes in acute ischemic stroke patients treated with reperfusion therapy is still unclear. Moreover, the use of pre-treatment collaterals in patient selection and prognosis is relatively underappreciated in clinical settings. A focused review of the literature was performed on the various methods of collateral evaluation and the role of collateral status in acute ischemic stroke patients receiving reperfusion therapy. We discuss the methods of evaluating pre-treatment collaterals in clinical settings. The patient selection based on collateral status as well as the prognostic and therapeutic value of collaterals in acute ischemic stroke, in settings of intravenous thrombolysis or endovascular therapy alone, and bridge therapy, are summarised. Recommendations for future research and possible pharmacological intervention strategies aimed at collateral enhancement are also discussed. Collaterals may play an important role in identifying acute ischemic stroke patients who are likely to benefit from endovascular treatment in an extended time window. Future neuroscientific efforts to better improve our understanding of the role of collaterals in acute ischemia as well as clinical studies to delineate its role in patient selection and acute stroke prognosis are warranted.This article is protected by copyright. All rights reserved.