Diabetes mellitus is the most common metabolic disorder worldwide. In Germany, more than 6 million people suffer from diabetes, Apart from pathological alterations to the renal, cardiovascular, and nervous systems, as well as the eyes, hyperglycaemia is also associated with the development of a variety of skin diseases. Skin diseases in diabetes mellitus can occur in the pre-diabetic stage as well as in manifest diabetes. During the pre-diabetic stage, dermatological disorders are of particular diagnostic value. Necrobiosis lipoidica, for example, appears most commonly in the pre-diabetic stage. In both the pre-diabetic stage as well as in manifest diabetes, bacterial and mycotic infections of the skin are frequent. In rare cases, viral infections also occur. Other diabetes-associated skin disorders include bullosis diabeticorum, scleroderma diabeticorum, acanthosis nignicans, granuloma annulare dissiminatum, diabetic dermopathy, rubeosis diabeticorum, and pruritus diabeticorum. Furthermore, certain anti-diabetic treatments can actually cause characteristic skin disorders that the physician should be able to recognize. In this review, skin disorders often associated with diabetes mellitus are described, as well as how to treat them.