Objective: This study is the first attempt to use cardio-ankle vascular index (CAVI) for evaluation of systemic arterial stiffness in patients with idiopathic pulmonary arterial hypertension (IPAH). Design and method: 45 patients with IPAH, 32 patients with arterial hypertension (AH), 35 healthy persons adjusted by age were included in study. RHC, ECG, 6 minute walk test (6 MWT), echocardiography, blood pressure (BP) measurement and ambulatory BP monitoring, pulse wave elastic artery stiffness (PWVe) and muscular artery stiffness (PWVm), CAVI, NT-proBNP level were provided. The Spearman correlation, a linear regression and multivariable binary logistic analysis were performed to indicate the predictors associated with PWV and CAVI. Results: IPAH patients had significant (P < 0.001) shorter 6MWT distance and higher Borg dyspnea score than patients with AH (systolic/diastolic BP- 146.1 ± 3.7/94.2 ± 3.8mmHg) and control group - 330.2 ± 14.6 vs 523.8 ± 35.3 and 560.9 ± 30.2m respectively and 6.2 ± 1.8 vs 1.2 ± 2.1 and 0.9 ± 2.8 points. The PWVm and PWVe were highest in hypertensive patients - 10.3 ± 1.5 and 11.42 ± 1.70m/s. The control group and IPAH did not have significant differences in aorta BP, but PWVm/PWVe values were significant (P < 0.003/0.008) higher in IPAH patients, than in control group - 8.1 ± 1.9/8.49 ± 1.92vs6.63 ± 1.34/7.29 ± 0.87m/s. The CAVIs on both sides were significant lower in healthy subjects (5.91 ± 0.99/5.98 ± 0.87 right/left side). Patients with IPAH did not differ from AH patients by CAVIs in comparison with control group - 7.40 ± 1.32/7.22 ± 1.32vs7.19 ± 0.78/7.2 ± 1.1. PWVe did not correlate with any parameters except uric acid. PWVm correlated with uric acid (r = 0.58, P < 0.001), NT-proBNP (r = 0.33, P = 0.03) and male gender (r = 0.37, P = 0.013) at Spearman analysis, but not at multifactorial linear regression analysis. Unlike the CAVI correlated with age and parameters characterized functional capacity (6 MWT distance) and right ventricle function (NT-proBNP, TAPSE) at Spearman analysis and with age and TAPSE at multifactorial linear regression analysis. At binary logistic regression analysis CAVI > 8.0 at right or/and left side had correlation with age, 6MWT distance, TAPSE, but independent correlation was only with age (beta = 1.104,P = 0.008) and TAPSE (beta = 0.66,P = 0.016). Conclusions: Patients with IPAH had significant stiffer arteries than healthy persons and they were comparable with AH patients. Arterial stiffness evaluated by CAVI correlated with age and TAPSE in IPAH patients.