Diabetes mellitus (a group of metabolic disorders characterized by hyperglycemia) and periodontitis (a microbially induced inflammatory disorder that affects the supporting structures of teeth) are both common, chronic conditions. Multiple studies have demonstrated that diabetes mellitus (type 1 and type 2) is an established risk factor for periodontitis. Findings from mechanistic studies indicate that diabetes mellitus leads to a hyperinflammatory response to the periodontal microbiota and also impairs resolution of inflammation and repair, which leads to accelerated periodontal destruction. The cell surface receptor for advanced glycation end products and its ligands are expressed in the periodontium of individuals with diabetes mellitus and seem to mediate these processes. The association between the two diseases is bidirectional, as periodontitis has been reported to adversely affect glycemic control in patients with diabetes mellitus and to contribute to the development of diabetic complications. In addition, meta-analyses conclude that periodontal therapy in individuals with diabetes mellitus can result in a modest improvement of glycemic control. The effect of periodontal infections on diabetes mellitus is potentially explained by the resulting increase in levels of systemic proinflammatory mediators, which exacerbates insulin resistance. As our understanding of the relationship between diabetes mellitus and periodontitis deepens, increased patient awareness of the link between diabetes mellitus and oral health and collaboration among medical and dental professionals for the management of affected individuals become increasingly important.