Whole-blood viscosity is increasingly being recognized as a factor implicated in the vascular disease progression in high-risk chronic kidney disease patients. Intermittent hemodialysis and hemodiafiltration sessions, characterized by rapid volume changes and anemia correction by erythropoietin stimulating agents, are favorable conditions for enhancing whole-blood viscosity changes and consequently triggering cardiovascular events. To evaluate whole-blood viscosity changes induced by hemodiafiltration, a cross-sectional study has been performed in a group of 28 stable patients. In order to assess the impact of vessel size on whole-blood viscosity changes, we performed a dynamic whole viscosity analysis on a wide spectrum of shear rates reproducing vasculature hemorheologic conditions. Blood viscosity changes are dependent on patient characteristics, hemoglobin, and total plasma protein concentrations. Whole blood viscosity increases significantly during hemodiafiltration over the complete spectrum of shear rates. Dynamic whole-blood viscosity (WBV) increases up to 60%, predominantly at low shear rates in small arterioles and capillary beds. This observation underlines the potential pathogenic contribution of WBV increase in capillaries triggering cardiovascular events in the postdialysis period. Eight patients died from cardiovascular events. Higher WBV increase was noted in this group but did not reach statistical significance due to the insufficient power of the study. Hemorheological changes associated with WBV increase in capillary beds may contribute to aggravate silent tissue hypoxemia and precipitate cardiovascular events in chronic kidney disease patients. Prospective studies specifically designed and powered to evaluate the impact of WBV changes on cardiovascular events in dialysis patients are required.