BACKGROUND: Comprehensive data on the frequency of diabetes mellitus among hospitalized patients in Germany have not been published to date. METHODS: Among all inpatient cases aged ≥20 years that were documented in the German DRG statistics for 2015-2017, we analyzed the frequencies of five types of diabetes (type 1, type 2, other/pancreatic diabetes, "rare diabetes" with an ICD code of E12 or E14, gestational diabetes) and of prediabetes, stratified by sex and age group. The presence of any of these conditions was ascertained from the corresponding ICD-10 code among the main diagnoses (reasons for admission) or secondary diagnoses. We also compared the length of hospital stay, in-hospital mortality, and the frequency of various categories of main diagnosis in cases with and without diabetes in each age group. RESULTS: In the period 2015-2017, approximately 18% of the 16.4 to 16.7 million inpatient cases carried a main or secondary diagnosis of diabetes (in 2017: type 2, 17.1%; type 1, 0.5%). Diabetes was more common in male cases than in female cases (in 2017: type 2, 19.7% vs. 14.8%; type 1, 0.5% vs. 0.4%). In 2017, the greatest difference in length of hospital stay between patients with and without diabetes was for patients with type 1 diabetes aged 40-49 (7.3 vs. 4.5 days), while the greatest difference in in-hospital mortality was for patients with type 2 diabetes aged 70-79 (3.7% vs. 2.8%). From the age of 30 (age category 30-39), diseases of the cardiovascular system, and from the age of 50 (age category 50-59), diseases of the respiratory or urogenital systems were more frequently listed as a reason for admission in cases with than in those without diabetes. CONCLUSION: The fact that diabetes is twice as prevalent in hospitalized cases as in the general population underscores the high morbidity associated with the disease and the greater need of persons with diabetes for in-hospital care, as the population of multimorbid diabetes patients continues to grow older.