Periodontal diseases result from the response of the host's periodontal tissue to the bacterial toxins present in dental plaque. Several systemic diseases have been shown to influence the course and severity of periodontal diseases by altering the inflammatory response of the host. This paper focuses on the manifestations and dental management of periodontal diseases when these types of systemic conditions, including diabetes mellitus, hormonal changes of pregnancy and puberty, HIV-associated infection, and various blood dyscrasias, are present.