A growing amount of epidemiologic, experimental, and clinical evidence has linked infection as a risk factor to variousatherosclerotic diseases including acute myocardial infarction and cerebral infarction. Bacteremic infections with and without endocarditis carry a high risk for both stroke and acute myocardial infarction. During the last decade, chronic bacterial infections such as Chlamydia pneumoniae and dental infections have been associated as risk factors for various atherosclerotic diseases. These chronic bacterial infections are risk factors for acute cardiovascular events, but they may also have some role in the etiopathogenesis of atherosclerotic process itself. There are many known mechanisms that might explain the observed association of infection and atherosclerotic diseases, but it is probable that these mechanisms are complex and multifactorial and probably differ from infection to infection and from patient to patient. Infection theory is by no means against classic risk factor theory in the etiopathogenesis of atherosclerosis. Infection may also act as a synergistic risk factor together with classic risk factors in the development of various atherosclerotic diseases.