Diabetes mellitus (DM) is a heterogeneous group of disorders characterized by a high serum glucose level and by disturbances of carbohydrate and lipid metabolism. It is estimated that 11 million persons in the United States have DM, 90% of whom have non-insulin-dependent DM. At least 30% of persons with diabetes have some type of cutaneous involvement during the course of their chronic disease. This review classifies the cutaneous Undings in DM into four categories: (1) skin diseases with strong to weak association with DM; (2) cutaneous infections; (3) cutaneous manifestations of diabetic complications; and (4) skin reactions to diabetic treatment. Each of these categories is reviewed as well as the pathophysiology of the normal and diabetic basement membrane for a better understanding of the cutaneous manifestations of DM. Learning objective: At the conclusion of this learning activity, participants should be able to describe the four basic categories of cutaneous involvement in cases of diabetes mellitus including (1) skin diseases with strong to weak association with diabetes mellitus, (2) cutaneous infections, (3) cutaneous manifestations of diabetic complications, and (4) skin reactions to diabetic treatment.