In the present study, the frequency of sites exhibiting gingival inflammation and periodontal tissue breakdown was assessed in one group of 46 individuals (19-25 years old; test group T) who had suffered from diabetes mellitus (Type 1) for 10 years or more, and in another group of 41 non-diabetic controls (18-26 years old; control group C). Each individual was examined regarding oral hygiene status, gingival conditions, probing depths, probing attachment levels and gingival recessions. The interproximal marginal bone level was assessed in bitewing radiographs. No significant differences were found between the 2 groups regarding their oral hygiene status, frequency of sites with probing depths of greater than 3 mm and the position of the interproximal alveolar bone margin. The mean distance between the cemento-enamel junction (CEJ) and the interproximal bone crest was in group T, 0.91 +/- 0.14 (SD) mm and in group C, 0.95 +/- 0.18 (SD) mm. About 80% of the individuals in both groups were free from signs of marginal bone loss and only 1 subject in each group had greater than 6 sites with definitive bone loss. The group of diabetic patients had higher frequencies of inflamed buccal/lingual gingival units, gingival recessions and sites with attachment loss of greater than or equal to 2 mm. Most of the sites (85%) with attachment loss were located at the buccal and lingual surfaces. There were no significant correlations between the periodontal variables and the duration of diabetes, insulin dosage and HbA1 level. Individuals with both retinopathy and nephropathy had significantly more gingival inflammation than diabetic individuals without complications.