In humans, the vitamin D receptor (VDR) gene has been localized to the chromosomal locus 12q13-14. The gene is composed of a minimum of nine exons. Hereditary 1,25-dihydroxyvitamin D resistant rickets (HVDRR) known as vitamin D dependent rickets type II is a rare autosomal recessive disease that arises as a result of mutations in the gene encoding the VDR. Genetic factors play a key role in determining bone mass, which is an important predictor of osteoporosis. Recently, polymorphism at the VDR locus has been implicated as a genetic marker for bone mineral density. Vitamin D receptor gene start codon polymorphisms, and 3'-end region polymorphisms may modulate bone density.