SUMMARYA 71-year-old lady presented with a symptomatic left cerebral occipital lobe infarct. With a history of paroxysmal atrial fibrillation a cardioembolic source was initially postulated. Prior significant bleeding while anticoagulated precluded warfarin therapy. Further investigations revealed a critical left internal carotid stenosis with a persistent fetal origin of the left posterior cerebral artery. She was successfully treated surgically and suffered no further ischaemic events. Physicians encountering posterior circulation stroke should be aware of this potentially treatable important diagnosis. BACKGROUND