Experimental and clinical data implicate calcium and parathyroid hormone (PTH) in the development of prostate cancer. However, epidemiologic data on the role of these variables in prostate health are sparse. We examined the relationship between serum levels of calcium, PTH, and prostate-specific antigen (PSA), an established marker of prostate growth, in a large, population-based study using multivariate linear regression. We studied 1,273 men in National Health and Nutrition Survey 2005 to 2006 who were >or=40 years of age and who were without clinical prostate cancer. Adjusted for age, race, body mass index, and serum levels of 25-hydroxyvitamin D, serum levels of PTH were significantly positively correlated with serum PSA (P = 0.01). Serum levels of PTH and calcium each were correlated significantly with free PSA (P = 0.05 and 0.008, respectively). The percentage of men who had elevated serum levels of PTH (PTH, >or=66 pg/mL) was significantly greater among African American men (19.2 versus 9.6%, P = 0.04). Compared with men whose PTH was at the lower end of the reference range, the predicted PSA for men with a PTH of 66 pg/mL was increased 43%. These findings support the hypothesis that serum calcium and serum PTH stimulate prostate growth in men without clinical prostate cancer and have implications for the use of PSA as a screening tool for prostate cancer.