Vitamin D inhibits prostate cancer cell growth, angiogenesis, and metastasis. These actions are mediated by the vitamin D receptor. We examined associations between prostate cancer risk and five polymorphisms in the VDR gene: four single nucleotide polymorphisms (FokI, BsmI, ApaI, and TaqI restriction sites) and the polyadenylic acid microsatellite. Specifically, we genotyped population-based samples of young African Americans (113 cases and 121 controls) and Whites (232 cases and 171 controls) and members of 98 predominantly White families with multiple cases of prostate cancer. Among Whites, there was no evidence for association between prostate cancer risk and alleles at any of the five polymorphic sites regardless of how the men were ascertained. Moreover, estimated five-locus haplotype frequencies were similar in White cases and controls. Among African Americans, prostate cancer risk was associated with homozygosity for the F allele at the FokI site (odds ratio 1.9, 95% confidence interval 1.0-3.3). In addition, estimated haplotype frequencies differed significantly (P < 0.01) between African American cases and controls. These findings need replication in other studies of African Americans. Homozygosity for the F allele at the FokI site is more prevalent in the African American population than in U.S. Whites. If the FokI association noted here were causal, this difference could account for some of the disease burden among African Americans and some of the excess risk in African Americans compared with Whites.