The purpose of this paper is to assimilate epidemiological evidence for the prevalence of periodontal disease in human populations, and for comprehensive understanding of the disease for health care providers. Periodontal disease is a pathological condition affecting the supporting structures of teeth. It is characterised by a bacterial challenge that can instigate a destructive host response leading to periodontal attachment loss, bone loss and ultimately, possible tooth loss. The specifics of the disease process are obscured by our incomplete understanding of the role of various risk factors. Periodontal epidemiology literature lacks consistency in methodology of research, which includes various definitions for periodontal disease and health; different approaches to measuring periodontal indices of pocket depth, and attachment loss; inconsistent study designs and lack of adjustments to known risk factors. These inconsistencies do not allow for effective comparison of epidemiological studies, which is essential to find strong associations of risk factors with periodontal disease, which in turn is necessary for the interpretation of risk and causality. This paper will address several areas within the topic of periodontal disease epidemiology, including definitions of periodontal disease instituted by researchers, approaches to epidemiological studies in periodontitis, and risk factors in periodontal disease. Consideration is given to aspects of design and analyses relevant to evaluation of reports in the literature. For the clinical practitioner this review provides a theoretical framework to approach patients with comprehensive knowledge of not only the disease presentation, but also the environmental factors that govern past history, present condition and future response to treatments and interventions.