Breast cancer strikes one out of eight women in Switzerland. The increase in breast cancer incidence over the past 70 years parallels an enormous increase of man-made, persistent chemicals in our environment; some of which have endocrine-disrupting properties in wildlife and/or in animal models. Epidemiological evidence is strong that a woman’s risk to get breast cancer is linked to her reproductive history and with that to the changes in her hormonal milieu. Exogenous hormones have also been shown to increase breast cancer risk, however, a causative link between exposure to endocrine disruptors and human disease is difficult establish as many of these compounds are ubiquitous and no unexposed controls exist. The synthetic estrogen, diethylstilbestrol (DES), that was given to pregnant women for three decades, was banned because it was linked to a vaginal carcinoma in their daughters. It has now been shown that not only women who have taken the drug themselves have increased breast cancer risk but also their daughters who were exposed in utero. This indicates that breast cancer risk can be affected by endocrine disruption not only in the adult but already in utero. Evidence from animal models is accumulating that perinatal exposure to environmentally relevant, low doses of a related compound, bisphenol A (BPA), alters breast development and increases breast cancer risk. Given the prevalence of endocrine-disrupting agents they deserve our attention.