Diseases of the oral cavity and related structures, either local or systemic, may have profound physical and emotional effects on a patient. In order to effectively manage these conditions, it is necessary that dentists have a basic understanding of diseases throughout the body. Such an obligation is tempered only by the extent to which diseases relate to the dental profession's anatomic field of responsibility or have clinical implications for office personnel, and the extent to which diseases require modification of dental therapy or alter the prognosis. A primary organic abnormality is typically reflected in the findings of radiographic, laboratory, and tissue studies. From the analysis of a large number of such profiles, certain patterns emerge that are sufficiently characteristic to suggest a specific diagnosis or groups of differential diagnoses for abnormalities that may prompt a request for urgent dental care.