We studied 21 consecutive patients from the Lausanne Stroke Registry, who had first-ever ischemic stroke and lone atrial fibrillation, with a standard protocol of investigations including brain CT, and non-invasive cardiac and arterial tests. Rarity of associated risk factors and extracranial; arterial disease, presence of distal intracerebral occlusions on early angiography, and topography of cerebral infarct suggested that cardioembolism was the cause of stroke, though echocardiographic evidence for an atrial thrombus was uncommon. There was no recurrence during a post-stroke 14-day phase, during which anticoagulant and antiaggregant therapies were systematically avoided. Though low, the main risk of stroke recurrence was 0.99 per 100 patient-years during a mean follow-up period of 4.8 years, including a mean duration of anticoagulant therapy of 2.3 years in 18 patients. On the other hand, no death, severe cardiac events, or disabling anticoagulation-related hemorrhages occurred.