Insulin-like growth factors (IGFs) are potent mitogens involved in the regulation of cell proliferation and apoptosis. The action of IGFs is mediated through a specific cell membrane receptor (IGF-IR), and the interactions between IGFs and this receptor are regulated by IGF-binding proteins (IGFBPs). IGFBP-3 is one such protein which either suppresses or enhances the actions of IGFs. Findings from most in vitro studies suggest that IGFBP-3 inhibits breast cancer cell growth and facilitates apoptosis, but clinical studies have found that high levels of IGFBP-3 in breast cancer tissues are associated with unfavourable prognostic indicators of the disease, such as large tumour size, low levels of steroid hormone receptors, elevated S-phase fraction and DNA aneuploidy. To further examine the role of IGFBP-3 in breast cancer recurrence and survival, we conducted the following nested case-control study. From a cohort of 1,000 women treated surgically for primary breast cancer, we consecutively selected 100 patients who developed recurrent disease after surgery and 100 age-and year of diagnosis-matched patients who had no relapse. Concentrations of IGFBP-3 in breast tissue extracts were determined with an ELISA. Inverse correlations of IGFBP-3 were revealed with estrogen receptor expression and patient age but not with tumour size or S-phase fraction. Levels of IGFBP-3 in breast tissues were slightly higher in the recurrent patients than in controls, but the differences were not statistically significant. No significant association was found between IGFBP-3 and breast cancer recurrence. Survival analysis, however, indicated that the risk of death was increased with higher IGFBP-3 levels, and the association was independent of other prognostic markers. In conclusion, our results demonstrate that high levels of IGFBP-3 are associated with unfavourable prognostic features of breast cancer.