Stenosis and thrombosis are the most important complications leading to vascular access failure in hemodialysis (HD). Aiming for an early access dysfunction diagnosis and elective repair of the failing access, the DOQI guidelines recommend that all HD patients undergo a program of regular monitoring and surveillance. The K/DOQI 2000 update identifies specific types of evaluation for dialysis accesses. First nephrologists should examine patients by inspecting, ausculting and palpating the access at least every 4-6 weeks when patients are not being dialyzed. In addition, access surveillance should be regularly performed by various techniques, i.e. urea recirculation test, dialysis venous pressure measurement and access blood flow assessment. Recently many methods have been proposed and implemented. Ultrasound dilution is the most commonly used. This technique relies on the change in ultrasound velocity when blood is diluted with a normal saline bolus at a known dialyzer blood flow rate, after the lines have been reversed. Following the use of blood ultrasound dilution, multiple technologies have been implemented for access flow measurement with line reversal, i.e. hematocrit (Hct) dilution, thermodilution, conductivity variation assessment. There are three other methods that do not require line reversal: i.e. transcutaneous access flow (TQA) assessment, glucose pump test (GPT) and the variable flow Doppler. Finally, duplex scanning can provide both the anatomy and blood flow of the access. With a Qa <600 mL/min or <1000 mL/min, but reduced by 25% in 4 months, K/DOQI suggest performing angiography and eventual elective repair.