Several studies have reported an association between chronic obstructive pulmonary disease (COPD) and periodontal diseases. However, a large-scale population-based cohort study was previously absent from the literature. Therefore, we evaluated the risk of periodontal diseases in patients with COPD in a nationwide population.From the National Health Insurance claims data of Taiwan, we identified 22,332 patients with COPD who were newly diagnosed during 2000 to 2010. For each case, two individuals without COPD were randomly selected and frequency matched by age, sex, and diagnosis year. Both groups were followed up till the end of 2011.The overall incidence of periodontal diseases was 1.19-fold greater in the COPD group than in the comparison group (32.2 vs 26.4 per 1000 person-years; 95% confidence interval [CI] 1.15–1.24). Compared with non-COPD patients, the adjusted hazard ratios of patients with COPD increased with the number of emergency room visits (from 1.14 [95% CI 1.10–1.19] to 5.09 [95% CI 4.53–5.72]) and admissions (from 1.15 [95% CI 1.10–1.20] to 3.17 [95% CI 2.81–3.57]). In addition, the adjusted hazard ratios of patients with COPD treated with inhaled corticosteroids (1.22, 95% CI 1.11–1.34) and systemic corticosteroids (1.15, 95% CI 1.07–1.23) were significantly higher than those of patients not treated with corticosteroids.Patient with COPD are at a higher risk of developing periodontal diseases than the general population. Our results also support that the risk of periodontal diseases is proportional to COPD control. In addition, patients who receive corticosteroid treatment are at a higher risk of developing periodontal diseases.