Human prostate cells contain receptors for 1α,25-dihydroxyvitamin D, the active form of vitamin D. Prostate cancer cells respond to vitamin D₃ with increases in differentiation and apoptosis, and decreases in proliferation, invasiveness and metastasis. These findings strongly support the use of vitamin D-based therapies for prostate cancer and/or as a second-line therapy if androgen deprivation fails. The association between either decreased sun exposure or vitamin D deficiency and the increased risk of prostate cancer at an earlier age, and with a more aggressive progression, indicates that adequate vitamin D nutrition should be a priority for men of all ages. Here we summarize recent advances in epidemiological and biochemical studies of the endocrine and autocrine systems associated with vitamin D and their implications for prostate cancer and in the evaluation of vitamin D₃ and its analogs in preventing and/or treating prostate cancer.