BACKGROUND: The use of menopausal hormone therapy (MHT) may interact with genetic variants to influence colorectal cancer (CRC) risk. METHODS: We conducted a genome-wide gene-environment interaction between single nucleotide polymorphisms and the use of any MHT, estrogen-only, and combined estrogen-progestogen therapy with CRC risk, among 28,486 postmenopausal women (11,519 cases and 16,967 controls) from 38 studies, using logistic regression, two-step method, and 2- or 3-degree-of-freedom (d.f.) joint test. A set-based score test was applied for rare genetic variants. RESULTS: The use of any MHT, estrogen-only and estrogen-progestogen were associated with a reduced CRC risk [odds ratio (OR) with 95% confidence interval (95% CI) of 0.71 (0.64-0.78), 0.65 (0.53-0.79), and 0.73 (0.59-0.90), respectively]. The two-step method identified a statistically significant interaction between a GRIN2B variant rs117868593 and MHT use, whereby MHT-associated CRC risk was significantly reduced in women with the GG genotype [0.68 (0.64-0.72)] but not within strata of GC or CC genotypes. A statistically significant interaction between a DCBLD1 intronic variant at 6q22.1 (rs10782186) and MHT use was identified by the 2-d.f. joint test. The MHT-associated CRC risk was reduced with increasing number of rs10782186-C alleles, showing ORs of 0.78 (0.70-0.87) for TT, 0.68 (0.63-0.73) for TC, and 0.66 (0.60-0.74) for CC genotypes. In addition, five genes in rare variant analysis showed suggestive interactions with MHT (two-sided P < 1.2x10-4). CONCLUSION: Genetic variants that modify the association between MHT and CRC risk were identified, offering new insights into pathways of CRC carcinogenesis and potential mechanisms involved.