We examined several polymorphisms in the VDR gene, their associated haplotypes, and polymorphisms in the vitamin D-binding (group-specific component [GC]) protein and 1,25(OH)2D degradation enzyme (CYP24A1) genes in relation to breast cancer risk in a nested case-control study of postmenopausal women enrolled in a large prospective cohort. The gene discussed is CYP24A1; the disease is breast cancer.