In the present study, the authors look at an association of genetic variants within estrogen synthesis and signaling pathways and age at menarche (AAM) in Spanish women. They analyzed 9 polymorphisms in 6 different genes in 714 well-characterized postmenopausal women from Spain. They performed a quantitative trait locus study of these markers individually or in digenic combinations in relation to AAM. None of the studied markers, with the exception of the follicle-stimulating hormone receptor (P = .013), were significantly associated with AAM in the Spanish population, and no marker demonstrated an association of statistical significance after multiple testing corrections (P > .0055). In contrast, linear regression analysis suggests epistatic interactions including ESR1 and ESR2 loci in relation to AAM in the series (P = .003). The results suggest that epistatic interactions of ESR1 and ESR2 alleles could be associated with advancing AAM among Spanish women.