To study the influence of ER-alpha on mammographic density. We selected 87 healthy women (age 49.8 +/- S.D. 6.12 years). We obtained the body mass index (BMI), and a fasting blood sample for hormone determinations and DNA extraction. ER-alpha genotyping was carried out by PCR and digestion with a Pvull and Xbal restriction endonucleases. Mammographic density was assigned by the radiologist used three categories of fatty, average and dense. Mammographic density was significantly associated with estradiol (p = 0.04), estrone (p = 0.04), and FSH (p = 0.02). The BMI was not associated with Pvull and Xbal genotypes and marginally with mammographic breast density (p = 0.06). We did not observe compelling evidence of an association between variant alleles of genotypes estrogen receptors alpha and breast density.