Background Vessel wall adaptation to acute or chronic flow changes is regulated by shear stress (SS) at the endothelium. This hypothesis was tested in the brachial artery (BA) of patients receiving an arteriovenous fistula (AVF) for hemodialysis vascular access. Methods The acute and sustained effects were evaluated in 13 patients. Pre-operatively and postoperatively on predetermined time-points BA diameter and shear rate (SR) were measured. SS was calculated from whole blood viscosity and SR. Analysis was performed with Wilcoxon's test and ANCOVA multivariate analysis. Results Acutely, mean SS increased (475%, p<0.05), peak-to-peak SS decreased (37%, p<0.05) and peak SS remained constant. BA diameter increased (15%, p<0.05). After one year a further increase was observed (r=0.59, p<0.001), plus an increase in mean SS (r=0.78, p<0.001). Peak-to-peak SS remained constant. Conclusion Our results indicate that after AVF placement an acute increase in SS results in an acute increase of vessel diameter. However, one year of sustained high blood flow does not result in restoration of mean SS.