OBJECTIVE: Laboratory data suggest that several different vitamins may inhibit the growth of mammary cancers, however epidemiologic data on the relationship between vitamin supplement use and breast cancer are inconsistent. We examined the association between self-reported vitamin supplement use and breast cancer among black women and white women. DESIGN AND SETTING: The data came from a population-based, case-control study conducted in North Carolina between 1993 and 1996. Logistic regression models were used to calculate adjusted odds ratios (ORs) for breast cancer associated with the use of multivitamins or individual vitamin supplements. SUBJECTS: Eligible cases were aged 20 to 74, and approximately 40% of the study population were black women. The analyses included 861 cases and 790 controls. RESULTS: Among all women, there was little evidence for an association between any vitamin supplement and breast cancer. Modest inverse associations were observed among white women for use of multivitamins 95% confidence interval (CI): 0.59-1.12), vitamin C 95% CI: 0.54-1.14) and vitamin E 95% CI: 0.49-1.13). There was no evidence that vitamin supplements reduced the risk of breast cancer among black women. CONCLUSIONS: This study provided very limited support for the hypothesis that vitamin supplements may reduce the risk of breast cancer. Although dietary factors are likely an important influence in breast cancer aetiology, reductions in risk are most likely to be achieved through dietary modification rather than through vitamin supplementation.