Uridine diphospho-glucuronosyltransferase 1 (UGT1A1) is involved in estradiol glucuronidation, which may play a central role in the etiology of breast cancer. A common insertion/deletion polymorphism in the TATAA-box of the promoter region of UGT1A1 results in decreased initiation of transcription, and has been associated with breast cancer risk in different ethnic groups. In the present study, the role of the above genetic variation at the UGT1A1 locus in breast cancer susceptibility was investigated in a homogeneous population. Our case-control study included 136 women with breast cancer and 186 healthy female controls of Greek origin. The polymorphism A(TA)nTAA in the promoter region of UGT1A1 gene was studied using the Fragment Analysis Software of an automated DNA sequencer and three genotypes (homozygous 7/7, heterozygous 6/7, and normal homozygous 6/6) were identified. No significant associations were observed between the 7/7 genotype and breast cancer risk, indicating that further studies in Caucasian women are needed to elucidate the role of UGT1A1 polymorphism in breast cancer risk.