High flow extracranial to intracranial (HF EC-IC) cerebral revascularisation may be necessary in the management of complex skull base tumours and intracranial aneurysms. Vascular reconstruction techniques, in addition to direct clip reconstruction, have been described since the first successful bypass more than 50 years ago. Bypass grafting can be considered high flow when a radial artery or the saphenous vein is interposed between the extracranial carotids arteries and intracranial vessels. The decision as to whether to use a low flow or high flow bypass is determined by the anticipated cerebral blood flow needed and the availability of a supply source. In this review, we consider the indications, diagnostic evaluation strategies and long-term graft patency of HF EC-IC bypass surgery.