17β-Estradiol is important in maintaining bone structure, and regulation of its synthesis plays an important role in the development of postmenopausal osteoporosis. We and others have demonstrated associations between variation in the CYP19A1 gene (encoding aromatase) and areal bone mineral density (aBMD) phenotypes in women. In the present study 33 tag polymorphisms were genotyped across the CYP19A1 gene in a population of 1,185 Caucasian postmenopausal women to test the association between sequence variations, total DXA hip aBMD, and circulating 17β-estradiol levels. An in silico bioinformatics analysis was performed for single nucleotide polymorphisms (SNPs) associated with aBMD to identify putative functional effects, while linkage disequilibrium analysis of these SNPs was undertaken with previously published sequence variants. Five SNPs located in the central third of the gene were strongly associated with total-hip aBMD after adjustment for age (P = 0.006-0.013). A haplotype analysis of these five SNPs revealed an association between the haplotype C-G-G-G-C and increased aBMD (P = 0.008) and the haplotype A-A-A-A-A and a decreased aBMD (P = 0.021). The haplotype frequency was 9.0% for C-G-G-G-C and 15.4% for A-A-A-A-A, with the variation in mean total-hip aBMD explained by the haplotype analyses being 5% and 7%, respectively. None of these polymorphisms was significantly associated with circulating 17β-estradiol levels. In conclusion, common genetic variations within the CYP19A1 gene are significantly associated with aBMD in postmenopausal Caucasian women.