Cytochrome P-450 1A1 (CYP1A1) is involved in the 2-hydroxylation of estrogens and mammary carcinogens into 2-hydroxy catechol metabolites. Many commonly occurring single nucleotide polymorphism (SNP) are reported in CYP1A1 in various populations that include, isoleucine to valine substitution at 462 codon in heme binding region in exon 7 (A to G transition at position 2455; M2), threonine to asparagine substitution at codon 461 (C to A transversion at position 2453; M4), T to C transition at 3801 position (M1) and T to C transition at position 3205 (M3) in 3' non-coding region. Epidemiological studies have shown inconsistent patterns between CYP1A1 polymorphism and breast cancer risk among various populations. Most of the studies have shown significant association between CYP1A1 genotype polymorphism and breast cancer risk. The present investigation was therefore undertaken to investigate the association of M1, M2, M3 and M4 polymorphisms and their subsequent contribution in premenopausal and postmenopausal women with breast cancer risk in north Indian women. Genomic DNA was isolated from case controls and breast cancer patients, specific segments of genomic DNA were amplified and restriction fragment length polymorphism (RFLP) was performed. CYP1A1 expression and catalytic activity were also assessed in premenopausal and postmenopausal case controls and patients. Polymorphism at M1, M2 and M4 alleles was detected and odds ratio for W/M1 and M1/M1 was calculated as 1.07 (95% CI, 0.59-1.87) and 0.74 (95% CI, 0.28-1.96) respectively. Odds ratio for W/M1 and M1/M1 alleles in premenopausal and postmenopausal women was 1.09 (95% CI, 0.45-2.49)/0.62 (95% CI, 0.10-2.66) and 1.60 (95% CI, 0.60-4.22)/1.06 (95% CI, 0.22-7.33) respectively. Odds ratio for W/M4 and M4/M4 allele was 1.20 (95% CI, 0.65-2.24)/4.55 (95% CI, 0.44-226.2) and 0.96 (95% CI, 0.36-2.64)/4.51 (95% CI, 0.23-273.0) respectively in total and premenopausal women. In postmenopausal women odds ratio was calculated as 1.16 (95% CI, 0.45-2.94) for M4/W but it could not be detected for M4/M4 since this genotype was not found in any postmenopausal case controls. Odds ratio for W/M2 genotype was calculated 0.57 (95% CI, 0.28-1.02), 1.06 (95% CI, 0.40-2.47) and 0.33 (95% CI, 0.12-0.89) respectively for total, premenopausal and postmenopausal women, however, in any group the odds ratio for M2/M2 could not be detected as M2/M2 genotype was not found in breast cancer patients. Polymorphism at M1 and M4 alleles was not found significantly associated with breast cancer risk and only wild type genotype was found in case controls and patients for M3 allele. Lack of protective association between CYP1A1 M2 genotype was also observed, however, in postmenopausal women a significant protective association with breast cancer risk was found (odds ratio, 0.33; 95% CI, 0.12-0.89; P-value 0.03). Similarly, no significant alteration in CYP1A1 expression and catalytic activity was observed in wild type and variant genotypes both in premenopausal and postmenopausal patients as compared with their respective controls. The results obtained from the present investigation thus suggest that probably CYP1A1 (M1, M2, M3, and M4) polymorphism alone does not play a significant role in the breast cancer risk in north Indian women.