Diabetes mellitus is the most frequent metabolic disorder. Just under 5 million people suffer from this disease in Germany. Four types of diabetes mellitus are distinguished: type 1 diabetes, type 2 diabetes, other specific diabetes forms, and gestational diabetes. Many characteristics of diabetes mellitus including skin changes are already manifest in the "prediabetic" stage when glucose tolerance is limited so that every elevation of blood sugar levels must be considered pathological. Changes in skin due to diabetes mellitus can be categorized into four disease groups: skin infections, skin diseases found overly frequently in association with diabetes mellitus, skin alterations due to diabetic complications, and reactions to antidiabetic treatment.