The Japan Collaborative Cohort Study for Evaluation of Cancer Risk (JACC Study) was planned in the late 1980s as a large-scale cohort study of persons in various areas of Japan. In the present study, we conducted a nested case-control study and examined associations of breast cancer risk with serum levels of insulin-like growth factors I and II (IGF-I, IGF-II), as well as insulin-like growth factor binding protein-3 (IGFBP-3), among women who participated in the JACC Study and donated blood at the baseline. Sixty-three women who died or suffered from breast cancer were examined. Two or three controls were selected to match each case for age at recruitment and the study area. Controls were alive and not diagnosed as having breast cancer at the diagnosis date of the cases. Associations between the serum IGF-I, IGF-II, IGFBP-3 and breast cancer risk were evaluated using a conditional logistic regression model. In premenopausal Japanese women, IGF-I showed a marginal negative dose-dependent association with the breast cancer risk (trend P= 0.08), but any link disappeared on taking into account IGFBP-3 (trend P= 0.47), which was likely to be inversely associated with the risk. In postmenopausal women, IGFBP-3 showed a marginal dose-dependent association with the risk (trend P= 0.06). Further studies are needed to confirm these findings.