Background: Androgens have an anti-proliferative effect on endometrial cells. Human androgen receptor (AR) gene contains two polymorphic short tandem repeats of GGC and CAG, and a single-nucleotide polymorphism on exon 1 that is recognized by the restriction enzyme, StuI. Prior studies have shown that the lengths of the CAG and GGC repeats are inversely and linearly related to AR activity and associated with endometriosis and endometrial cancer. However, little is known about the single nucleotide polymorphism of the AR gene.Thus, we investigated whether these AR polymorphisms are risk factors for endometriosis.Materials and Methods: The genetic distributions of these polymorphisms were investigated in blood samples from 100 endometriosis patients and healthy controls.The allelic profiles were analyzed by polymerase chain reaction (PCR), PCR-restriction fragment length polymorphism (PCR-RFLP) and analyzed statistically.Results: The observed frequencies of GG, GA and AA genotypes of the G1733A polymorphism were 0.14, 0.68 and 0.18, respectively, for the patient group and 0.68, 0.3, and 0.02, respectively, for the control group. Allele frequencies were 0.48 and 0.83, respectively, for the patient and control groups for the G allele (wild type) and 0.52 and 0.17, respectively, for the patient and control groups for the A allele (mutant). Statistical analysis of these results indicated significant differences between the two groups (p=0.00014).Conclusion: These results indicated for the first time that the androgen receptor G1733A polymorphism is strongly associated with increased risk for endometriosis.