Objective: Increased arterial stiffness (AS) has been shown to predict cardiovascular mortality in patients with essential hypertension (EH). Ambulatory arterial stiffness index (AASI) was proposed as a surrogate measurement method for determination of AS. Although, some authors showed prognostic value of AASI, this is still a controversial issue. Our aim was to analyze AASI in 66 normotensive subjects (NT) and 114 patients with EH (divided in stage1 (47), stage 2 (41) and stage 3 (26)). Design and Methods: Detailed clinical exam was performed in all patients. Blood pressure (BP) was measured using mercury sphygmomanometer (RR) and ambulatory blood pressure monitor (ABPM) Spacelabs 90207 following the ESH/ESC guidelines. AASI was defined as 1 minus the regression slope of diastolic over systolic BP values obtained from ABPM. Results: NT were the youngest and had the lowest values of BMI (p0.05). The highest values of AASI were determined in stage 1 (0.3920.054) and NT (0.3860.036) being significantly different from results obtained in stage 2 and 3 (0.3690.042 ; 0.3620.048, respectively ; p¼0.01). Significant differences were observed between NT, stage1, 2 and 3 in pulse pressure values (PP) obtained using either RR (41.67.9 vs. 46.28.5 vs.51.612.3 vs.55.113.8, respectively ; p<0.0001) or ABPM (44.56.0 vs.49.18.9 vs.48.56.5 vs.54.09.8, respectively ; p¼0.0002). Conclusion: The highest AASI values were obtained in the youngest and in subjects with lowest values of BP (NT and stage 1). On contrary, PP values gradually and significantly increased from the NT to the stage 3 group. Obtained AASI values in all groups were below the proposed cut-off values of 0.5 and 0.7 for younger and older, respectively. Our results did not confirm important clinical value of AASI, and PP provide more useful data. Definitive validation of AASI should await further studies with direct measurements of AS.