The present investigation was performed to study the frequency of recurrence of periodontitis in diabetic subjects, who, prior to the initiation of a 5-year period of monitoring, were treated for moderate to advanced periodontal disease. 20 patients with diabetes, type 1 (IDDM) or type 2 (NIDDM) and 20, sex and age matched, controls with similar amounts of periodontal tissue destruction, were selected for the study. Following a screening examination, all patients were subjected to non-surgical periodontal therapy (oral hygiene instruction, supra- and subgingival scaling). 3 months later, the baseline examination for the study was performed. This included assessments of several parameters such as: number of teeth, plaque, gingivitis, probing pocket depth and probing attachment level. 6 months after the baseline examination, all 40 subjects were recalled for a 2nd examination. Sites which at this 6-month examination exhibited bleeding on probing, and had probing depth > 5 mm, were scheduled for additional surgical therapy (modified Widman flap). Following this selective additional therapy, the main period of monitoring was initiated. During this period, a plaque control program was repeated every 3 months. Re-examinations regarding plaque, gingivitis, probing depth and probing attachment level were performed 12, 24 and 60 months after the baseline examination. The findings from the examinations disclosed that diabetics and non-diabetics alike, treated for moderately to advanced forms of adult periodontitis, during a subsequent 5-year period, were able to maintain healthy periodontal conditions. Thus, the frequency of sites which exhibited signs of recurrent disease was similar in the 2 study groups.