Breast cancer development is related to genes regulating cell cycle progression such as CCND1, CDK7, and ESR1. We conducted a hospital-based case-control study to evaluate the role of genetic polymorphisms in these genes in breast cancer development among Korean women. Questionnaire data and samples were obtained from 864 incident breast cancer cases and 723 controls recruited from 1995 to 2002. Four single nucleotide polymorphisms (SNPs) in three genes were genotyped by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry [CCND1 Ex4-1G>A (rs9344), CDK7 Ex2-28C>T (rs2972388), ESR1 P325P Ex4-122G>C (rs1801132), and ESR1 T594T Ex8+229G>A (rs2228480)], and their associations with breast cancer risk were assessed. The odds ratios (ORs) and 95% confidence intervals (CIs) were estimated by unconditional logistic regression analysis adjusted for age, education, age at the first full-term pregnancy, and family history of breast cancer. Women carrying the CDK7 TT genotype had increased risk of breast cancer (OR, 1.4; 95% CI, 1.1-1.7). There was no significant association between breast cancer risk and the genetic polymorphisms of CCND1 and ESR1. However, when CDK7 and ESR1 P325P were combined, women carrying both the CDK7 TT and ESR1 P325P CC genotypes showed increased breast cancer risk (OR, 1.7; 95% CI, 1.1-2.5; P for trend, <0.01). In conclusion, our findings suggest that the combined genotypes of CDK7 and ESR1 are associated with breast cancer risk among Korean women.