One of the traits of type I and II diabetes lies in the presence of extensive rheological disorders. Rheological changes appear during infancy, mainly in type I diabetes: decreased red cell deformability, leukocyte rigidity, monocyte activation, alteration in microvessel flux (sludge) and functions. Such disorders are however sensitive to insulin and metabolic correction for a long period. Macrorheological disorders develop at the time of puberty and when lipid changes and vascular complications appear (hypertension, visceral obesity, atherosclerosis). Such changes have potent effects on diabetic arteriopathy, as shown by altered TcPO(2). Numerous medical teams are taking into account red cell aggregation measurements reflecting post-capillary flux behavior. In addition, a proposed score may be used based on fibrinogen, hematocrit, triglycerides as viscosity acting factors, and endothelial markers, Willebrand factor and VCAM-1. An increased score is an indication of suspected distal functional alteration of microvessels.