Extracranial to intracranial internal carotid artery bypass surgery with vein is well described for a number of diverse conditions. They provide high blood flow with good initial patency. However, long term patencies for specific graft types remains unknown. This is an analysis of consecutive interposition saphenous vein bypass cases between the common carotid artery (CCA) and the intracranial internal carotid artery (ICA) where the distal anastomosis was placed end-to-end immediately proximal to the posterior communicating artery in 55 patients undergoing 57 bypass procedures (bilateral in 2 cases). Twenty-five patients underwent grafting for planned vessel obliteration where the pathology required vessel sacrifice. Twenty-eight patients had bypass grafting for stroke risk reduction in the setting of threatening stroke and 4 patients had bypass grafts for emergency revascularisation in the setting of stroke in evolution. Patients were assessed preoperatively and at follow-up with modified Rankin scores. Procedural related complications included a 7% mortality and 7% functional decline. Early graft occlusion occurred in 5% of grafts leading to death in each case. A further patient died of rupture at the distal anastomosis site. In surviving patients, patency was present in 100% at last follow-up (mean 5 years and maximum 11 years) with no patient sustaining new hemispheric ischemic events. One patient developed a delayed asymptomatic stenosis within the vein graft requiring stenting. Because of the high initial management risks this technique of common carotid to intracranial internal carotid artery saphenous vein bypass surgery should be reserved for patients at considerable risk by alternate management. However, once the acute postoperative period is past the bypass appears to be robust and capable of supplying the entire distribution of a normal internal carotid artery.