Periodontitis has been called the "sixth complication of diabetes mellitus." It is well-established that long-term hyperglycemia can lead to damage of various end organs including the heart, eyes, kidneys, nervous system, vascular system, and periodontium. Research has also shown that active periodontitis can also worsen glycemic control. This course will discuss the links between periodontal disease and diabetes mellitus and aid in clinical decision-making to care for patients with diabetes mellitus and periodontal disease.