The periodontal status of 25 patients with non-insulin dependent diabetes mellitus (NIDDM) (age range 58 to 76) was investigated and compared with 40 non-diabetic control subjects (age range 59 to 77). Surfaces with visible plaque and bleeding after probing, calculus, recessions, and pathological pockets were examined. The total attachment loss was calculated as a sum of recessions and pockets in millimeters. Mesial and distal bone loss was measured from panoramic radiographs and mean alveolar bone loss was calculated. Periodontal disease was considered advanced when mean alveolar bone loss was over 50%, or 2 or more teeth had pockets > or = 6 mm. Microbiological analysis comprised the detection of Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis, and Bacteroides forsythus by a polymerase chain reaction (PCR) method. Patients with NIDDM had significantly more often advanced periodontitis than control subjects, 40.0% and 12.5%, respectively. Diabetic patients did not harbor more pathogens than the control subjects. The HbA1C level deteriorated in patients with advanced periodontitis, but not in other patients with NIDDM, when compared to the situation 2 to 3 years earlier. Advanced periodontitis seems to be associated with the impairment of the metabolic control in patients with NIDDM, and a regular periodontal surveillance is therefore necessary.