A patient undergoing external carotid artery therapeutic embolization for obliteration of a dural arteriovenous malformation suddenly developed a large occipital artery to vertebral artery shunt. A devastating stroke was averted because the appearance of the shunt was observed by fluoroscopy, the embolization was stopped, and the shunt verified on a subsequent angiogram. The risk of external carotid artery embolization without constant fluoroscopic control is emphasized.