This paper evaluates the current information on the relationship between oral disease (specifically periodontitis) and atherosclerosis/coronary heart disease (CHD) to determine whether the information is sufficient to conclude that periodontitis is a risk factor for atherosclerosis/CHD. As background for this evaluation, the term "risk factor" is defined, and the 3 criteria used to establish exposures as risk factors are reviewed. In addition, epidemiologic criteria for defining an exposure as causal are presented. The available evidence then is evaluated according to the criteria for causality, which are extensions of the criteria for establishing a risk factor. This review is done in the context of the relationship between atherosclerosis/CHD and inflammation. A number of findings are briefly reviewed that link inflammation and atherosclerosis/CHD, such as: 1) prior flu-like symptoms were more common in cases of myocardial infarction than in concurrently sampled controls; 2) high levels of cytomegalovirus antibody titers were associated with elevated carotid intimal-medial wall thickness 18 years later; 3) prior infection with cytomegalovirus was a strong independent risk factor for restenosis after coronary atherectomy; 4) dental infections were more common in cases of cerebral infarction compared to community controls matched on age and sex; and 5) the gingival index was significantly correlated with fibrinogen and white cell counts in periodontal patients and controls, adjusted for age, smoking, and socioeconomic status. Three case-control studies and 5 longitudinal studies investigating the relationship between dental conditions and atherosclerosis/CHD are reviewed in terms of strength of associations, consistency of associations, specificity. of associations, time sequence between exposure and outcome, and degree of exposure and outcome. Related to the last criterion, new findings are presented which indicate that the extent of the periodontal infection, a measure reflecting microbial burden, also is related to onset of new CHD events. Our previously published model describing the potential biological mechanisms underlying the associations found is reviewed. This model places the associations into a context of an intrinsic or acquired hyperinflammatory monocyte trait that results in a more intense inflammatory response to lipopolysaccharide (LPS) challenges, such as periodontal infections. This hyperinflammatory response may promote atheroma formation and thromboembolic events. finally, new findings from ongoing animal studies are presented, indicating that high fat diets in atherosclerotic-susceptible mice induce greater inflammatory responses to Porphyromonas gingivalis challenges. We conclude that the available evidence does allow an interpretation of periodontitis being a risk factor for atherosclerosis/CHD. This conclusion, however. is made with some qualifications. While the associations found across a wide variety of subjects are remarkably consistent, for the most part they are represented by incidence odds ratios around 2.0. While this level of association would result in oral conditions contributing to a large number of CHD cases, it is possible that associations of this magnitude are due to bias in the study designs. In addition, some studies report that periodontitis is associated with all-cause mortality and low birth weight infants. These multiple associations detract from the credibility of periodontitis as a risk factor, as specificity of association is more often related to causality. However, all-cause mortality may largely be driven by mortality from cardiovascular events: and some exposures, such as smoking. are indeed risk factors for multiple conditions. On the other hand, current findings regarding the associations between oral conditions and atherosclerosis/CHD imply that the criteria for causality may be met in the not-too-distant future.