This review assesses the strength of evidence relating periodontal disease and atherosclerotic disease (ischemic heart disease, peripheral arterial disease, and ischemic stroke). Periodontal disease and atherosclerotic disease may be linked causally, or their relationship could be explained, wholly or partially, by common risk factors. Many potential pathways for the relationship have been postulated. This article focuses on evaluating the overall body of evidence, according to the following standard causal inference criteria: strength of association, dose-response relationship, time sequence, consistency, specificity, biologic plausibility, and independence from confounding. Each criterion is reviewed and evaluated against the existing literature. In summary, the overall strength of evidence for causal criteria for the relation between periodontal disease and atherosclerotic disease is as follows: The magnitude and consistency of the association is stronger for ischemic stroke (and is low for ischemic heart disease), some evidence for dose response exists, time sequence has been established with more evidence for stroke, and there is definitely biologic plausibility for all these associations. Independence from confounding is also stronger for ischemic stroke and peripheral arterial disease. Specificity is not established for any of these associations, as there are multiple risk factors for atherosclerotic disease; however, specificity is not considered an important criterion for causality. Because the underlying pathogenesis of atherosclerosis is common across the diseases, it is likely that if additional studies show consistent associations, periodontal disease may be an important independent causal risk factor for atherosclerotic disease, especially for ischemic stroke.