Introduction: Genome-wide association studies (GWAS) have revealed associations with endometriosis at seven genomic regions 1,2. The key SNP (rs13394619) on chromosome 2 is located within GREB1 which is a critical regulator of hormone-dependent breast cancer growth and increased GREB1 expression has been reported in endometriosis. Methods: We imputed genotypes across the GREB1 region using recent reference panels from the 1000 Genomes project and genotyped the key SNP and related SNPs in a subset of ~600 individuals from the GWAS data set to evaluate the accuracy of imputation. We also collected endometrial tissues from 157 women with or without endometriosis for GREB1 gene expression analyses using the Fluidigm qPCR platform. Results: Imputation results for common SNPs showed high concordance with true genotype data. For the gene expression study, we did not observe any significant changes in GREB1 expression in cases compared to controls. However, we observed a small but significant difference (p=0.046) in GREB1 expression between the tissues in proliferative phase and secretory phase. We also genotyped the key SNP (rs13394619) on chromosome 2 and conducted eQTL analysis to examine if there is any effect of this key SNP on the GREB1 gene expression in the endometrial samples. Our results showed a trend of small increase in GREB1 expression in the individuals carrying the risk allele for endometriosis. However, this change was not significant after multiple testing corrections. Conclusion: Further studies with larger sample size in each genotype group are required. As SNPs most strongly associated with disease risk are generally located in non-coding regions, key SNPs in regulatory regions of the genome will be prioritized for further analysis to examine the functional role of these SNPs on gene regulation.