Human epidemiological studies and experimental animal data strongly suggest that xenobiotics with estrogenic activity may participate in to the increasing incidence of breast cancer, the most frequent cancer all around the world. Several reports have since 15 years reported positive correlations between blood or peritumoral adipose tissue levels of persistent organic compounds including organochloride pesticides and breast cancer risk. Moreover, fetal or perinatal exposition to low doses of such endocrine disruptors induce premalignant or malignant transformation of adult mammary gland in rodents. However, this environmental endocrine disrupter hypothesis still needs to be demonstrated. Further human studies are needed which will consider the exposition window, the association of several xenoestrogens, the molecular mechanisms involved and the possible individual genetic susceptibility in order to identify pertinent biomarkers and to define acceptable environmental concentration levels for agricultural or industrial chemical new products to be used.