The aim of this study was to investigate the effects of hemorheological factors on the development of hypertension in diabetic children without retinopathy and persistent microalbuminuria. Arterial blood pressures were measured in 46 diabetic children and were compared with those of 29 healthy non-obese and 32 obese age- and sex-matched children. Higher systolic (SBP) (109.0+/-13.0 mmHg) and diastolic blood pressure (DBP) (74.3+/-9.5 mmHg) were obtained in diabetics (independent of age, sex, duration, and control degree of diabetes), when compared with non-obese children (SBP: 97.9+/-10.3 mmHg, DBP: 74.3+/-9.5 mmHg; p<0.01, p<0.05, respectively). No significant DBP and SBP difference was found between diabetics and obese children. When compared with non-obese children, blood viscosity, plasma viscosity, serum viscosity, serum albumin, and plasma fibrinogen values were found elevated in diabetics and were correlated with SBP and DBP. Serum haptoglobin levels and lipid profile were normal. The multivariate discriminant analysis demonstrated plasma viscosity and fibrinogen to be the most important variables related to the development of hypertension. The results of this study revealed that: (1) arterial blood pressures are high in diabetic patients independent of age, sex, duration of diabetes, control degree of diabetes, and lipid profiles; (2) arterial blood pressure levels in diabetic children are affected primarily from changes of plasma viscosity and fibrinogen; and (3) a common mechanism might play a role in the pathogenesis of hypertension in obese and diabetic children.