Abstract On the basis of glycosylated hemoglobin (HbAIC)values, 22 type I (insulin-dependent) diabetic adults were grouped into patients with near normal (HbAt1c≤7.7%) and Poor (HbAtc≥9.9%) metabolic control. A total of 44 subgingival sites were examined for Actinobacillus actinomycetemcomitans, black-pigmented Bacteroides species and Capnocytophaga species. No significant difference could be demonstrated between patients in the 2 test groups with regard to periodontal condition. Neither age of diabetic patients nor duration of diabetes mellitus influenced the periodontal parameters. In both test groups, pocket depth of 4 mm or more (≥4 mm) was found to be significantly associated with increased swelling, bleeding after probing and amount of marginal plaque. Proportionally high %s of cultivable A. actinomycetemcomitans (mean 4.3%; range 2.8–5.8%), Bacteroides gingival (33.2% and 34.6%) and Bacteroides intermedius (mean 4.2%; range 0.001–13.5%) were isolated from diseased periodontal pockets. In diabetic patients with poor metabolic control, B. intermedius was isolated from diseased periodontal pockets with a mean % of 7.2%, range 0.3–12.5%. Independent of the degree of metabolic control, low %s of Capnocytophaga species were isolated from diseased and healthy periodontal pockets, mean 0.9% (range 0.003–3.9%) and mean 1.4% (range 0.04–4.9%), respectively. It was concluded from this study that metabolic control seems to have no direct effect on the periodontium. Furthermore, the role of Capnocytophaga species in the pathogenesis of infectious periodontal disease in type I diabetic patients seems to be overestimated. However, A. actinomycetemcomitans and blackpigmented Bacteroides species may be important pathogens in periodontal disease in type I diabetic patients, as they are known to be in non–diabetic periodontal patients.