The aim of this study was to analyse periodontal disease experience in 40- to 70-year-old, sex-matched insulin-dependent diabetics and non-diabetics. The study involved 83 diabetics and 99 non-diabetics. The clinical and radiographic examination comprised recordings of number of teeth, presence of plaque, gingival conditions, probing pocket depth and alveolar bone level (main variable). Diabetics aged 40 to 49 years had more periodontal pockets > or = 6 mm and more extensive alveolar bone loss than non-diabetics in the same age-group. There was also a significantly higher number of subjects belonging to classification groups with severe periodontal disease experience among diabetics in that age-group. In the age-groups 50-59 and 60-69 years, no major differences were found. The disease duration in these 3 age groups was 25.6 years, 20.5 years and 18.6 years, respectively, and the age of onset thus appears to be an important risk factor for future periodontal destruction.