A number of studies suggest an association between periodontal disease and cardiovascular disease, pulmonary disease, diabetes,and pregnancy complications. Presently, the data must be regarded as preliminary. Additional large-scale longitudinal epidemiologic and interventional studies are necessary to validate these associations and to determine whether the associations are causal. The goal of this article is to review the history of this concept, describe the biologically plausible circumstances that may underlie these potential associations, and provide a summary of the published literature that supports or refutes them.