INTRODUCTION: There are gaps in our knowledge about differences in arterial stiffness (AS) and cardiorespiratory fitness (CRF) in adults with and without Down syndrome (DS). PURPOSE: To describe and compare AS and CRF in adults with DS versus adults without DS. METHODS: Fourteen adults with DS (27±5 yrs) and 14 adults without DS (27±5 yrs) participated in this study. An inform consent and a health screening questionnaire was completed by each participant and/or legal guardian. After familiarization, participants rested lying for 5-10 minutes before the measurements were taken. Brachial and central systolic and diastolic blood pressure (BSP; BDP; CSP; CDP), central augmented pressure (AP), augmentation index (AIx), AIx normalized at 75 beats/min ([email protected]) and AS (carotid-femoral pulse wave velocity (cfPWV)) were measured by using the SphygmoCor Xcel device (SphygmoCor XCEL, AtCor Medical). To assess the CRF, all participants performed a maximal treadmill test. Respiratory gas-exchange was measured breath-by-breath with an automatic gas analysis system (Metasys TR-plus, Brainware SA, La Valette, France). RESULTS: Non-DS participants were taller and had a lower BMI than the DS group (all p < .05). The CRF of the DS group was lower than the non-DS group (VO2 peak = 29.4±6.3 vs. 51.5±11.3 ml/kg/min; p < .001). Non-significant differences were found for BSP/BDP (DS = 116.31 ± 10.9/68.4 ± 9.3 vs. Non-DS = 123.43 ± 8.8/71.6 ± 6.6 mmHg; all p > .050); CSP/CDP (DS = 103.6 ± 8.5/61.1 ± 9.3 vs Non-DS = 107.0 ± 7.6/71.6 ± 6.6 mmHg; all p > .050) and cfPWV (DS = 5.5 ± .6 vs. Non-DS= 5.8 ± .7 m/sec; p = .191). The AP (DS = 6.4 ± 2.7 vs Non-DS = 1.8 ± 3.2 mmHg; p = .002); AIx (DS = 18.1 ± 6.3 vs Non-DS = 4.9 ± 10.3; p = .001) and the [email protected] (DS = 12.3 ± 8.8 vs Non-DS= -1.6 ± 11.7; p = .002) were significantly higher in the DS group. CONCLUSIONS: Despite having lower CRF and higher BMI, adults with DS presented similar values of central and peripheral blood pressure than the Non-DS group. Nevertheless, the DS group showed higher AP, AIx and [email protected] values, which may be due to a higher aortic wave reflection and arterial stiffness. Partially supported by: MINECO (DEP2017-86862-C2-1-R) & FPCEE Blanquerna (APR-FPCEE19/20).