The relationship between diabetes mellitusand oral health status was determined in Pirna Indians from the Gila River Indian Community in Arizona. This tribe of native Americans has the world's highest reported incidence and prevalence of non‐insulindependent (type 2) diabetes mellitus. The probing attachment level, alveolar bone loss, age, sex, Calculus Index, Plaque Index, Gingival Index, fluorosis, and DMFT as well as the diabetic status was assessed in 1,342 Pirna Indians who were at least partially dentate. The prevalence and severity of destructive periodontal disease was determined by measuring probing attachment loss and radiographically apparent interproximal crestal alveolar bone loss, two independent but correlated indicators of periodontal destruction. Only diabetic status, age, and the presence of subgingival calculus were significantly associated with both increased prevalence and greater severity of destructive periodontal disease in this population. Diabetic status was significantly and strongly related to both the prevalence and severity of disease after adjusting for the effects of demographic variables and several indices of oral health including the Plaque Index. Subjects with type 2 diabetes have an increased risk of destructive periodontitis with an odds ratio of 2.81 (95% confidence interval 1.91 to 4.13) when attachment loss is used to measure the disease. The odds ratio for diabetic subjects was 3.43 (95% confidence interval 2.28 to 5.16) where bone loss was used to measure periodontal destruction. These findings demonstrate that diabetes increases the risk of developing destructive periodontal disease about threefold. Furthermore, diabetes increases the risk of developing periodontal disease in a manner which cannot be explained on the basis of age, sex, and hygiene or other dental measures. Periodontitis should be considered a potential complication of diabetes in evaluation of patients.J Periodontol 1991; 62:123–130.