The health effects related to bisphenol A (BPA) and its exposure sources have undergone extensive investigation, but no consensus has been reached. Hitherto, the major source of human BPA exposure considered in the literature remains food-contact material. However, the chlorine present in drinking water may react with BPA to form chlorinated derivatives (ClxBPA), which have indeed been shown to have a heightened level of estrogenic activity. In this study, we have evaluated colostrum concentrations of BPA and ClxBPA in order to confirm our hypothesis according to which BPA water contamination leads to ClxBPA human exposure. BPA and its ClxBPA were assessed through online solid-phase extraction coupled to ultra high-performance liquid chromatography tandem mass spectrometry (SPE-UPLC-MS/MS) using the isotope dilution method in the colostrums of 21 women who had completed a water exposure questionnaire. BPA was detected in 19 colostrums and its ClxBPA in 21 colostrums. Mean concentrations were 1.87 ± 1.38 ng mL(-1) (n = 19) for BPA, 1.87 ± 1.23 ng mL(-1) (n = 7) and 1.56 ± 0.74 (n = 18) ng mL(-1) for 2,2'-Cl2BPA and 2,6-Cl2BPA, respectively, and 0.68 ng mL(-1) (n = 1) for trichloro-BPA. These findings confirm our hypothesis that ClxBPA should be taken into account in human health risk assessment.