The polymorphisms of the estrogen receptor (ER) gene defined by the restriction enodonucleases PvuII and XbaI have recently been reported to be associated with bone mineral density (BMD) in postmenopausal women. To investigate the possible relation of the PvuII and XbaI restriction fragment-length polymorphisms of the ER gene with BMD in Danish postmenopausal women, two studies were undertaken: 1) a cross-sectional study of 499 postmenopausal women, where the ER genotypes and alleles were related to BMD of the hip, spine, and lower forearm; and 2) a longitudinal study of 101 postmenopausal women followed up for 18 years. In the latter study, late postmenopausal bone loss in the hip and spine was determined over a period of 6 years in women (mean age of 63 to 69 years), and long-term postmenopausal bone loss in the lower forearm was determined over a period of 18 years in women (mean age of 51 to 69 years). Genotyping was performed through the restriction cleavage of polymerase chain reaction-amplified genomic DNA with the two restriction enzymes, PvuII and XbaI. Restriction fragment-length polymorphisms were represented as P or p (PvuII) and X or x (XbaI), with the lower case letters signifying the presence of the restriction site. The frequencies of the ER genotypes were similar to previously published genotype frequencies in Caucasian and Asian populations. No significant effect of the ER genotypes or alleles on BMD was found at any site, nor was there a relation between ER genotypes and the rate of bone loss either in the hip and spine over 6 years, or in the lower forearm over 18 years. In conclusion, we could not demonstrate any major effect of the ER gene polymorphisms on BMD or rate of bone loss in healthy postmenopausal Danish women.