Abstract BACKGROUND High dietary sodium intake may induce a small, yet physiologically relevant rise in serum sodium concentration, which associates with increased systolic blood pressure. Cellular data suggest that this association is mediated by increased endothelial cell stiffness. We hypothesized that higher serum sodium levels were associated with greater arterial stiffness in participants in the Systolic Blood Pressure Intervention Trial (SPRINT). METHODS Multivariable linear regression was used to examine the association between baseline serum sodium level and (i) pulse pressure (PP; n = 8,813; a surrogate measure of arterial stiffness) and (ii) carotid–femoral pulse wave velocity (CFPWV; n = 591 in an ancillary study to SPRINT). RESULTS Baseline mean ± SD age was 68 ± 9 years and serum sodium level was 140 ± 2 mmol/L. In the PP analysis, higher serum sodium was associated with increased baseline PP in the fully adjusted model (tertile 3 [≥141 mmol] vs. tertile 2 [139–140 mmol]; β = 0.87, 95% CI = 0.32 to 1.43). Results were similar in those with and without chronic kidney disease. In the ancillary study, higher baseline serum sodium was not associated with increased baseline CFPWV in the fully adjusted model (β = 0.35, 95% CI = –0.14 to 0.84). CONCLUSIONS Among adults at high risk for cardiovascular events but free from diabetes, higher serum sodium was independently associated with baseline arterial stiffness in SPRINT, as measured by PP, but not by CFPWV. These results suggest that high serum sodium may be a marker of risk for increased PP, a surrogate index of arterial stiffness.