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Vitamin D deficiency or high levels of parathyroid hormone (PTH) appear to be emerging risk factors for hypertension. This study examined whether serum concentrations of 25-hydroxyvitamin D [25(OH)D] and PTH were independently associated with blood pressure and the presence of hypertension or prehypertension among the United States adults.Cross-sectional data from 7228 participants (aged ≥20 years) in the 2003–2006 National Health and Nutrition Examination Survey were analyzed. The least square means and the regression coefficients of systolic blood pressure, diastolic blood pressure, and pulse pressure across quintiles of serum 25(OH)D and PTH were estimated by conducting multiple linear regression analyses. The adjusted prevalence ratios with 95% confidence intervals for hypertension and prehypertension were estimated using the log-binomial method.Among participants not taking blood pressure medications (n = 5414), the mean age- and sex-adjusted systolic and diastolic blood pressure decreased linearly across quintiles of serum 25(OH)D but increased linearly across quintiles of serum PTH (P < 0.001 for all); these relationships remained significant even after extensively adjusting for covariates. Similarly, across quintiles of serum 25(OH)D, the age-adjusted prevalence of hypertension and the adjusted prevalence ratios for both hypertension and prehypertension decreased linearly (P < 0.001 for all). In contrast, the prevalence of hypertension and prehypertension increased nonlinearly (P < 0.05 for both) and the adjusted prevalence ratios for hypertension increased linearly across quintiles of serum PTH (P < 0.001).Serum concentrations of 25(OH)D and PTH were independently associated with blood pressure and with the presence of hypertension or prehypertension among the United States adults, though casual relationships remain to be elucidated.