Infections have long been recognized as a potential, if uncommon, cause of cerebrovascular disease. In recent years, with the growing recognition of the importance of inflammation in atherosclerosis, there has been renewed interest in the possibility that common infections may participate in the atherosclerotic process or lead to stroke through other mechanisms. Specific organisms that have been implicated include Chlamydia pneumoniae, herpes viruses, human immunodeficiency virus, Helicobacter pylori, and organisms associated with periodontal infections. This article outlines the epidemiological, pathological, and laboratory evidence that these infections may be associated with atherosclerosis and stroke. Although definitive proof of an association between a specific infection and stroke is generally lacking, the accumulating evidence does indicate that several types of infections may be among the modifiable risk factors that contribute to the risk of stroke.