The Japan Collaborative Cohort Study for Evaluation of Cancer Risk (JACC Study) was planned in the late1980s as a large-scale cohort study of persons in various areas of Japan. In the present study, we conducted anested case-control study and examined associations of breast cancer risk with serum levels of insulin-like growthfactors I and II (IGF-I, IGF-II), as well as insulin-like growth factor binding protein-3 (IGFBP-3), among womenwho participated in the JACC Study and donated their blood at the baseline. Sixty-three women who died orsuffered from breast cancer were examined. Two or three controls were selected to match each case for age atrecruitment and the study area. Controls were alive and not diagnosed as having breast cancer at the diagnosisdate of the cases. Associations between the serum IGF-I, IGF-II, IGFBP-3 and breast cancer risk were evaluatedusing a conditional logistic regression model. In premenopausal Japanese women, IGF-I showed a marginalnegative dose-dependent association with the breast cancer risk (trend P= 0.08), but any link disappeared ontaking into account IGFBP-3 (trend P= 0.47), which was likely to be inversely associated with the risk. Inpostmenopausal women, IGFBP-3 showed a marginal dose-dependent association with the risk (trend P= 0.06).Further studies are needed to confirm these findings.