Early case-control and cross-sectional studies demonstrating associations between chronic periodontitis and cardiovascular disease (CVD) were quickly followed by secondary analyses of data available from existing longitudinal studies, which indicated that individuals with periodontitis, as determined by clinical measures, were at greater risk for CVD events. Many of these studies contained large numbers of subjects and were adjusted for traditional risk factors. Within the last 18 months, one case-control study and one longitudinal study have reported finding positive associations that were not statistically significant. The earlier studies stimulated a number of studies focused on identifying potential biological mechanisms that might underlie this association. While still early in that process, such studies have implicated a systemic role for oral microorganisms and for the quality and quantity of the host inflammatory response as key biologic processes that may underlie the association of CVD with the clinical manifestation of periodontitis. It is a positive development when changes in our knowledge regarding biologic mechanisms result in reevaluation of past studies, and this reevaluation leads to new studies that incorporate the design elements demanded by this new knowledge. In that spirit, we conclude that all longitudinal studies reported to date can be characterized as follows: none were initially designed to actually test the association of interest; almost all were restricted to clinical measures of periodontitis to index the exposure and lacked measures of infectious burden and host response; and they used a variety of cardiovascular clinical events to index the outcome and did not include subclinical measures of atherosclerosis. In addition, the longitudinal studies that failed to show a significant association between periodontitis and CVD used the least sensitive and crudest clinical measures of periodontal disease. Based upon the current state-of-the-science, all previous studies should be viewed as lacking sufficiently sensitive and comprehensive measures of periodontal disease as a systemic exposure. Since the potential health care impact of this relationship might be extensive, it is time to enter the next phase of research by conducting molecular epidemiology studies that are appropriately designed to test our current understanding of the molecular and cellular mechanisms involved.