Prophylaxis and treatment of arterial embolism in high-risk patients includes therapy with antiplatelet drugs, anticoagulation, and vascular surgery. The prominent causes of cerebral ischemia are intraarterial emboli from atheromatous plaques and cardiac emboli. In patients with recent hemispheric transient ischemic attacks or minor stroke and ipsilateral high-grade internal carotid artery stenosis of 70 to 99% carotid endarterectomy has shown to be effective in prevention of major stroke or death. In the majority of patients with moderate atherosclerotic disease of the extracranial arteries as well as in patients with a cardiac source of emboli, no generally excepted therapy for primary and secondary prevention of cerebral ischemia or systemic embolism exists. The efficacy of antiplatelet drugs and anticoagulants in these patients is still investigated in a number of clinical multicenter studies. From the presently available data one can conclude that the antiplatelet agent acetylsalicylic acid in a dosage of 300 mg per day is effective in the secondary prevention of stroke and death in patients with preceding transient ischemic attacks, minor or major stroke and suspected artery-to-artery embolism from mild to moderate atherothrombotic carotid and vertebral artery disease. If there are no contraindications, we recommend anticoagulation in recurrent transient ischemic attacks not responding to antiplatelet drugs, in progressing stroke especially in the vertebrobasilar territory, in transient ischemic attacks in patients with rheumatic atrial fibrillation and left atrium thrombi, in minor stroke and proven cardiac embolism, in cerebral ischemia due to traumatic large vessel disease, and before and following elective cardioversion in patients with long-standing atrial fibrillation. A therapeutic dilemma still exists in patients with nonrheumatic atrial fibrillation; the presently available data are not sufficient to give recommendations whether aspirin or anticoagulants should be given for primary and secondary prevention of stroke and systemic embolism in these patients.