Abstract Background Chronic Obstructive Pulmonary Disease (COPD) is a preventable and treatable disease characterized by persistent respiratory symptoms and airflow limitation. It is currently one of the leading cause of death worldwide. Metabolic syndrome has been recognized as one of the most relevant clinical comorbidities associated with COPD. Diabetes is more prevalent in COPD than in the general population, ranging between 10.1-23.0%. However, the link between COPD and diabetes is much less clear. The aim of this study was to investigate the effect of COPD on diabetic patients, focusing on length of stay and in-hospital mortality. Methods The study considered all hospital admissions of diabetic patients aged over 65 years performed between January 2006 and December 2015 in Abruzzo, a region of Italy. Data were collected from all hospital discharge records. A 1:1 propensity score-matching algorithm was used to match patients with and without COPD, according to their baseline characteristics. Logistic regression analysis was performed to evaluate the risk of in-hospital mortality and prolonged length of stay among diabetic patients with COPD. Results A total of 140,556 ?patients were included: 18,379 with COPD and 122,177 without COPD. After matching procedure, 36,758 patients were included into the analysis: 18,379 with COPD and 18,379 controls. After matching, all the baseline characteristics resulted well balanced, with a standardized mean difference less than 10% for all the variables considered. COPD patients showed a higher risk of in-hospital mortality (OR: 1.10; 95%CI 1.01-1.20; p = 0.036) and length of stay over 15 days (OR:1.18; 95%CI 1.06-1.31; p = 0.002). Conclusions In a cohort of Italian patients, diabetic patients with COPD showed a higher risk of in-hospital mortality and prolonged length of stay compared with diabetic patients without COPD. Defining the causes of these differences would improve public health surveillance systems and policies. Key messages Diabetes is more prevalent in COPD than in the general population. Diabetic patients with COPD showed a higher risk of in-hospital mortality and prolonged length of stay compared with diabetic patients without COPD.