Diabetes and periodontitis are chronic inflammatory diseases and have a bidirectional relationship. Periodontitis is more prevalent and more severe in diabetic persons than in nondiabetic persons, and diabetes plays a crucial role in the pathogenesis of periodontitis. Also, periodontitis has shown elevated risk for hyperglycemia and insulin resistance. Thus, mutual management of the two conditions might be necessary. Periodontal therapy is effective in persons with diabetes and is associated with reduction of HbA1c. The present study reviews the mechanistic link between diabetes and periodontitis and the effects of periodontal treatment and can aid in educational planning to prevent periodontitis of diabetic persons.