A body shape index (ABSI) has been introduced as a marker of the relationship between body composition and all-cause mortality. However, until now, the relationships between ABSI and vascular structure and function have not been evaluated. The aim of this study was to investigate the association of ABSI with vascular structure and function in Spanish adults with intermediate cardiovascular risk. This cross-sectional study analyzed the data of 2354 subjects [age, 35-74 years (median, 62.0 years [range, 56.0-67.0 years]), 61.9% men] enrolled into the MediAte Risk management (MARK) study. ABSI was calculated by using the following formula: ABSI = waist circumference (m)/[body mass index × height (m))]. Vascular function was assessed by measuring cardio-ankle vascular index (CAVI) with the VaSera device and brachial ankle pulse wave velocity (baPWV) by using a validated equation. Vascular structure was assessed by measuring carotid intima-media thickness (IMT) by ultrasonography. Median value of ABSI was 0.083 (range, 0.081-0.090), mean CAVI was (8.5 ± 1.2), and median IMT was 0.727 (range, 0.672-0.799). The values of ABSI and CAVI were higher in men. After adjusting for confounders, ABSI was positively associated with CAVI, baPWV, and average mean IMT. Thus, for each unit increase in ABSI, CAVI increased by 0.16 units, baPWV by 0.25 m/s, and IMT by 0.033 mm. In the logistic regression analysis, the odds ratio of ABSI was > 1 for high CAVI ≥ 9, baPWV ≥ 15 m/s, and IMT ≥ 0.90 mm in the overall subject group, and in the sex- and age-specific (> 62 years, ≤ 62 years) subgroups, after adjusting for confounders. The area under the receiver-operating characteristic curve of the ABSI was 0.631 (95% confidence interval [CI], 0.608-0.654) for CAVI ≥ 9, and 0.617 (95% CI, 0.593-0.641) for high baPWV ≥ 15 m/s. ABSI showed a positive association with vascular structure and function, independent of other confounders that might influence weight and fat mass distribution in Spanish subjects at intermediate cardiovascular risk.Trial Registration: ClinicalTrials.gov Identifier: NCT01428934 (registered: September 2, 2011; last updated: September 8, 2016).