A microsurgical anastomosis between the superficial temporal artery and a cortical branch of the middle cerebral artery was carried out in 11 cases with internal carotid occlusion. This treatment was attempted following angiography of the intra- and extracranial cerebral arteries. After the microsurgical procedure for creating an extra-intracranial arterial anastomosis selective angiography of the homolateral external carotid circulation was performed. The analyses of the serial arteriograms showed, that a) a considerable blood supply from the external carotid circulation through the additional collateral pathway to the territory of the middle cerebral artery is possible, b) the extent of the area of the middle cerebral artery supplied by the superficial temporal artery is not only dependant upon a pressure gradient between the external carotid and the middle cerebral artery circulation, but also by the different anatomical variations of the middle cerebral artery.