Background: The prevalence of periodontal diseases, gingivitis and periodontitis, is higher in diabetic patients and can have severe functional and esthetic consequences early in their lives. Aim: To evaluate the prevalence of periodontal disease in type 1 diabetics, aged between 18 and 30 years old, living in Santiago de Chile. Subjects and methods: One hundred male and female type 1 diabetics were examined. Glycated hemoglobin A1c, microalbuminuria, and fundoscopy were assessed in a sample of 52 subjects, separated in two groups according to the presence of periodontal disease. Results: The prevalence of gingivitis was 22%, periodontitis 41%. Only 37% of subjects were free of periodontal disease. When compared with patients without periodontal disease, in the group of patients with the disease there was a higher proportion of subjects with diabetes lasting more than 10 years (28 and 55% respectively) and a higher proportion of patients with chronic complications of diabetes (42 and 58% respectively). Conclusions: A high prevalence of periodontal diseases was observed in this sample of diabetic patients. A long history of diabetes and the presence of chronic complications were risk factors for these diseases in the analyzed sample (Rev Méd Chile 2002; 130: 402-408)