Objectives: The purpose of the study was to examine the association between diabetes mellitus and community periodontal index in Korean adults. Methods: The study populations were recruited by the Fifth Korea National Health and Nutrition Examination Survey. Study subjects were 10,411 who were examined oral examination, blood test, and aged over 19 years. Using multiple logistic regression analyses, the variables were adjusted for gender, age, household income, family history of diabetes, body mess index, smoking habit, and frequency of tooth brushing. Periodontal tissue examination of the subjects was performed and scored by Community periodontal index(CPI). Using probe, six teeth were examined for hemorrhage, plaque, and pocket depth and classified into $CPI_0$, $CPI_1$, $CPI_2$, $CPI_3$ and $CPI_4$. Healthy periodontal groups($CPI_{0-2}$) and periodontal disease groups($CPI_{3-4}$) were divided by the periodontal disease status. The definition of diabetes mellitus(DM) was decided by the diagnosis by the doctors and fasting blood sugar level. Those who were diagnosed as DM were included in DM group. The DM variables included normal blood sugar level, increased fasting blood sugar level, and DM blood sugar level. The DM variables were compared to periodontal disease blood sugar level and analyzed. Results: The periodontitis prevalence rate was 23.2%. Those who had diabetes mellitus accounted for 5.5% of the subjects. Those who had impaired fasting glucose accounted for 17.7% and 7.9% of subjects were diabetes mellitus by blood test. In the confirmed diabetes group by doctor, the periodontitis prevalence rate was significantly higher than the non-diabetic group. Diabetic group by blood test had the highest prevalence rate of periodontitis than those who had impaired fasting glucose group or normal group. After adjusting for gender, age, household income, family history of diabetes, body mass index, smoking habit, and frequency of tooth brushing, the risk of periodontitis in diagnosed diabetes mellitus was 1.57 times(95% CI; 1.27-1.94) higher than the normal group. In impaired fasting glucose group and diabetes mellitus group by blood test, the risk of periodontitis was 1.11 times(95% CI; 0.95-1.30) and 1.45 times(95% CI; 1.45-2.12) higher, respectively. Conclusions: There was a significant relationship between diabetes mellitus and periodontitis in Korean adults. These results suggest that diabetes mellitus is a risk factor for periodontitis.