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 findings 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.