AIMS: One previous study among women with established coronary heart disease found a gene-treatment interaction between the oestrogen receptor gene (ESR1) and hormone replacement in their association with high density lipoprotein cholesterol (HDL-c). We aimed to replicate these findings in a general population sample. METHODS AND RESULTS: Cross-sectional associations were assessed in a study of 3404 women from 23 towns across Britain who were aged 60-79 at the time of assessment and were described as white by the examining nurse. Women with the T-A haplotype [constructed from two single nucleotide polymorphisms (SNPs) in the first intron of ESR1: c454-397T > C (rs2234693) and c454-351A > G (rs9340799)], which was predicted to be associated with reduced oestrogen response, were more likely to have been past [per haplotype odds ratio 1.16 (95% CI 1.01, 1.33), P = 0.02] or to be current users [per haplotype odds ratio 1.19 (95% CI 0.99, 1.42), P = 0.05] of hormone replacement. However, there was no association between haplotype or either SNP and HDL-c or other cardiovascular disease risk factors and no statistical evidence of an interaction between hormone replacement use and haplotype or either SNP with respect to HDL-c or any other cardiovascular disease risk factors. CONCLUSION: Women with the T-A haplotype are more likely to use hormone replacement. However, genotyping of ESR1 rs2234693 or rs9340799 in post-menopausal women to tailor hormone replacement is unlikely to markedly improve cardiovascular risk.