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Ambulatory arterial stiffness index (AASI) is a parameter derived from ambulatory blood pressure (ABP) readings. It is calculated as 1 minus the linear slope of DBP on SBP. We tested its value in assessing arterial stiffness in dialysis patients.We performed a cross-sectional analysis of the baseline data from a cohort study. A total of 344 patients on maintenance hemodialysis from six tertiary hospitals were included. All patients underwent ABP monitoring and carotid–femoral pulse wave velocity (cfPWV) measurement. Clinical determinants of AASI were analyzed, and the ability of AASI for assessing arterial stiffness was compared with ambulatory pulse pressure (PP).Multiple regression analysis revealed that ambulatory PP (β = 0.003), current smoker (β = −0.069), age (β = 0.003) and ambulatory SBP (β = 0.001) were independent determinants of AASI. Ambulatory PP correlates better with cfPWV than AASI (r = 0.28 for AASI and 0.59 for PP; P for difference: <0.001). When cfPWV was treated as a categorical variable, receiver operating characteristic curve analysis also showed a more potent predictive value of PP over AASI (area under the curve: 0.64 for AASI, 0.80 for PP; P for difference: <0.001). Net reclassification improvement and integrated discrimination improvement analysis demonstrated no added predictive value of AASI to PP (net reclassification improvement = −2.2%, P = 0.26; integrated discrimination improvement = 0.001, P = 0.51). Sensitivity analysis in patients with more ABP readings (≥49) yielded similar results.For dialysis patients, AASI has very limited value in assessing arterial stiffness, whether used alone or added to PP. Our results suggest that this index should not be used as a surrogate marker of arterial stiffness for dialysis patients in future practice and studies.