The vitamin D receptor (VDR) was the first candidate gene to be studied in relation to osteoporosis, and most attention has focused on polymorphisms situated near the 3' flank of VDR. The aim of this study was to investigate the association about VDR gene Apa I polymorphism with bone mineral density (BMD) in postmenopausal women with osteoporosis. We studied a total of 136 postmenopausal women with a mean age of 56.36 +/- 10.29 years. Among them, a total of 75 had osteoporosis, 37 had osteopenia, and 24 had normal BMD. Venous blood samples were obtained for evaluation of bone metabolism and genotyping. The VDR Apa I genotype was determined by polymerase chain reaction-restriction fragment length polymorphism. BMDs at the lumbar spine and hip were measured by dual-energy X-ray absorptiometry. Postmenopausal women with aa genotype had significantly lower BMD values (grams per centimeter square) at lumbar spines compared to persons with AA genotype. Also, postmenopausal women with AA genotype had significantly higher serum Ca level than the subjects with aa genotype. In conclusion, our result may indicate that VDR Apa I gene polymorphism may be responsible for a important part of the heritable component of lumbar spine BMD in postmenopausal women, possibly related to impaired calcium absorption from the bowel.