Polymorphic alleles of key candidate genes such as CYP1B1, which are involved in oestrogen and xenobiotic metabolism, may contribute to the different risks of breast cancer observed for different populations.12–14,16–19 In the present study, we investigated CYP1B1 polymorphisms in a Ningxia Han Chinese population, and observed that the genotypes 119T/T and G/T are present at a significantly higher frequency (P = 0.001) in breast cancer patients than in control participants. This evidence concerns the gene CYP1B1 and breast cancer.