Diabetes mellitus is a disease in which the capillary basement membranes are substantially altered. This diabetic microangiopathy is characterized by a thickening of the basement membrane and changes in its permeability characteristic due to a disturbance in the production and distribution of its functional components. Glucose metabolism and insulin imbalance have been implicated in these basement membrane modifications. The authors describe normal capillary basement membrane architecture and then discuss how pathologic changes caused by diabetes mellitus are related to diabetic foot pathology.