To review recent data on the nature and pathobiology of periodontal infections and to elaborate how periodontal infections might increase susceptibility to some important systemic diseases and conditions. Medline literature search and websites of the American Academy of Periodontology and American Medical Association. Literature and data on periodontal diseases and their links to systemic diseases. Review of relevant information and data. Periodontal diseases, including gingivitis and periodontitis, are among the most common infections of humans. They are induced by bacteria and bacterial products of dental plaque and are characterised by inflammatory destruction of tooth-supporting connective tissues and alveolar bone. A growing body of scientific evidence has shown that severe periodontitis may enhance susceptibility to certain important systemic diseases and conditions, for example, cardiovascular disease, diabetes mellitus, adverse pregnancy outcomes, and pulmonary infections. The clinical implications of the emerging specialty of periodontal medicine for dental and medical practitioners are postulated. Periodontal diseases may be risk factors for cardiovascular disease, diabetes mellitus, adverse pregnancy outcomes, and pulmonary infections. Dental and medical practitioners should be aware of the clinical implications of these inter-relationships and treat affected patients in collaboration for better oral and general health.