The present study was designed to explore the association between estrogen receptor-alpha gene polymorphism and the risk of endometriosis by investigating the frequency of PvuII, XbaI, and thymine-adenine (TA) repeat polymorphisms in patients with and without endometriosis in a Korean population. Although there was no significant difference in the allele distribution and frequency of either PvuII or XbaI polymorphisms between endometriosis patients and control subjects, patients with stage I/II endometriosis showed a higher incidence of alleles with fewer (TA)n repeats (12-15 repeats) compared with controls.