Correlations with periodontitis have been reported for several diseases, although the biological mechanisms that might lead to these putative correlations are generally unclear. This paper describes the most robust of these associations, on the basis of an evaluation of research syntheses (meta-analyses and systematic reviews) available up to June 2011. This high-level evidence indicates that individuals with periodontitis have a significantly higher risk of various other problems, including cardiovascular disease, diabetes mellitus, respiratory disease and preterm low-birth-weight deliveries. For some conditions, treatment of periodontitis leads to a reduction in the rates of the other disease, lending further support to the concept that the association is reversible. An understanding of these correlations is important to allow dental health care providers to inform patients with periodontitis of their increased risks and to counsel such patients to seek additional medical assessment or intervention, as indicated.