Red blood cell (RBC) deformability is an important hemorheological parameter to determine the passage of RBC through narrow capillaries and the reduction of blood viscosity under high shear rates. Although it has been substantial evidence that diabetes mellitus (DM) and hypercholesterolemia increase the risk of coronary heart disease, the mechanism is unclear. In this study the relationship between hemorheological parameters and plasma cholesterol in type 2 diabetic patients (n=55, mean age 43.4+/-9.2 years) was examined. Type 2 diabetic patients were classified as normocholesterolemic (n=25; cholesterol less than or equal to 200 mg/dl) and hypercholesteroloemic (n=30; cholesterol > 200 mg/dl) subgroups. Hypercholesterolemic type 2 diabetic patients had the highest blood and plasma viscosity and the lowest RBC deformability. The results were significantly different from normocholesterolemic type 2 diabetic patients (p<0.001).