Background: Diabetes mellitus (DM) represents a major public health issue and a significant economic burden worldwide. It is associated with an increased rate of hospitalization and higher in-hospital mortality. Hospitalized diabetics often have a complex pattern of comorbidities that complicate management and worsen prognosis. Aims: The aim of this retrospective study was to identify the most common comorbidities in diabetic patients hospitalized in an Internal Medicine Department and evaluate the impact of diabetes on the length of hospital stay and mortality by sex and age. Methods: Between January 2017 and December 2023, 14,164 patients (50.7% men) were admitted to our Internal Medicine Unit. DM was defined according to the International Statistical Classification of Diseases and Related Health Problems (ICD) version 9 code 250. The main comorbidities associated with diabetic disease were identified and the length of hospitalization and mortality in diabetic patients stratified by gender and age were also examined. For the statistical analysis of categorical variables, the Chi-squared test was used, while continuous variables were analyzed using the Mann-Whitney U test or the Kruskal Wallis test. Results: Diabetes was present in 1462 (846 or 57.9% men, age 17-101 years) inpatients with a downward trend since 2019. In 193 (13.2%) it represented the main cause of hospitalization, without gender differences. Hypertension (34.0%), liver cirrhosis (19.7%), kidney disease (19.1%), respiratory failure or pneumonia (18.1%) and malignant tumors (15.0%) were the most frequent comorbidities. Patient age and number of not cardiovascular-related comorbidities showed to significantly impact hospital mortality in diabetics. Conclusions: Although the retrospective design and the use of administrative data represent major limitations, the study showed that diabetic patients present peculiar patterns of comorbidities which differently impact the length of hospitalization and hospital mortality. A better outpatient management of diabetes can reduce the number of hospitalizations by other causes and improve the outcomes and costs of those that are non avoidable.