Stroke is a heterogeneous disorder. A small number are due to hemodynamic insufficiency. In these cases, blood supply is sufficient at rest but unable to meet increased demand. This is demonstrated by loss of cerebrovascular reactivity (CVR) or increased oxygen extraction fraction (OEF). This may be improved by a superficial temporal artery to middle cerebral artery bypass. Whilst too small to completely replace cerebral blood supply, this is sufficient to augment existing blood flow to meet any increases in demand. Practically it has been difficult to demonstrate any reduction in stroke rate with intracranial revascularization. Only one of three randomized studies has shown a benefit. Two problems have been how hemodynamic insufficiency and symptomatic patients have been defined. Hemodynamic insufficiency can only be reliably demonstrated by changes in OEF and CVR. Symptomatic has traditionally described a patient who was had one or more strokes. However, in most cases these occur at the time of occlusion following which the patient remains stable. These patients are not necessarily at a high risk of future stroke as collaterals develop over time to compensate. We prefer to reserve the term symptomatic for those who have ongoing fluctuating symptoms after demonstration of carotid occlusion. This much smaller subset may still benefit from surgery in our view. Therefore although bypass surgery has relatively low morbidity, and high graft patency, extremely careful patient selection is essential for it to benefit patients, and unless there are both severe hemodynamic insufficiency and ongoing symptoms medical management is preferable.