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The cytochrome P 450 1A1 gene encoding a phase I metabolic enzyme appears to be a candidate for breast cancer risk. It is involved in the phase I detoxification of polycyclic aromatic hydrocarbons (PAHs) and 2-hydroxylation of estrogens and mammary carcinogens into 2-hydroxy catechol metabolites. Several studies have investigated polymorphisms in CYP1A1 and breast cancer risk with inconsistent results. We here carried out a population based case-control study of the CYP MspI (CYP1A1*1/M1) and Ile462Val (CYP1A1*2/M2) polymorphisms in CYP1A1 to clarify their importance in determining breast cancer susceptibility in a South Indian population. A total of 50 cases and 50 controls were genotyped for both polymorphisms. We also investigated putative interactions with exposure to pollution, radiation and intake of tobacco and CYP1A1 genotype and breast cancer risk using a case only study design. The genotype distribution of CYP1A1*1 in cancer patients was 6% for homozygous (CYP1A1 M1 [C/C], 34% for heterozygous CYP1A1 M1 [T/C] and 60% for wild type (CYP1A1 M1 [T/T] (OR: 0.583, CI-95% (0.252-1.348). The genotype distribution of M2 genotypes in patients was 24% of homozygous (CYP1A1 M2 [Val/Val], 4% for heterozygous (CYP1A1 M2 [Ile/Val] and 72% for wild type allele (CYP1A1 M2 [Ile/Ile] [OR: 0.720, CI-95% (0.606-0.856)]. Our results suggest that there is no significant correlation between CYP1A1 M1/ CYP1A1 M2 polymorphism and occurrence of breast cancer in South Indian women.