Given the disease burden of stroke, prevention is an important public health concern. Primary prevention is less effective than secondary prevention (as judged by the number needed to treat to prevent one stroke per year). Recent guidelines detail the evidence for primary prevention in stroke. About the use of aspirin as a preventive medication for stroke, in healthy people aspirin does not appear beneficial and thus is not recommended, but in people with high cardiovascular risk, or those who have had a myocardial infarction, it provides some protection against a first stroke. In those who have previously had stroke, treatment with medications such as aspirin, clopidogrel, and dipyridamole may be beneficial. The U.S. Preventive Services Task Force (USPSTF) recommends against screening for carotid artery stenosis in those without symptoms.