Background: The prevalences of both hypertension and vitamin D insufficiency are high in the United States. Recent clinical trials and animal studies have suggested that vitamin D insufficiency may be associated with elevated blood pressure. Objective: With cross-sectional data, we sought to determine whether vitamin D concentrations were related to systolic blood pressure (SBP) in the third National Health and Nutrition Examination Survey (1988-1992). Design: Blood pressure was classified with 5 categories from the Joint National Committee 7 with a sixth category added to distinguish participants with normotensive SBP (<110 mm Hg) from those with high-normal SBP (110-119 mm Hg). We used predicted marginals to estimate the conditional means of serum 25 hydroxyvitamin D [25(OH)D] and to test for trend across blood pressure categories. We used linear regression to explore the association between vitamin D, blood pressure, and age. Results: Lower 25(OH)D concentrations were associated with a higher blood pressure category in whites (P < 0.001); however, when controlling for age, the association was no longer significant. Concentrations of 25(OH)D>80 nmol/L decreased the age-related increase in SBP by 20% compared with participants having 25(OH)D concentrations < 50 nmol/L (P < 0.001). Only 8% of blacks had 25(OH)D concentrations > 80 nmol/L. Conclusions: SBP is inversely associated with serum vitamin D concentrations in nonhypertensive white persons in the United States. This observation provides a rationale for studies on the potential effects of vitamin D supplementation as a method to reduce SBP in persons at risk of hypertension. © 2008 American Society for Nutrition.