The results of the present study indicate that the periodontal condition of older Thais with uncontrolled diabetes is: (a) significantly improved 3 months after mechanical periodontal therapy with adjunctive systemic antimicrobial treatment, and (b) rapidly deteriorating without periodontal treatment. The effect of periodontal therapy on the glycemic control of older uncontrolled diabetics will require further studies that will have to include much larger sample sizes.