We hypothesize that the link between height and the risk of breast cancer may, to some extent, be accounted for by an association between maternal height and the risk of breast cancer. Unlike mothers of smaller stature, among taller mothers, maternal size does not impose constraints on fetal growth, thus allowing growth-enhancing pregnancy hormones, including estriol and insulin-like growth factors, to exercise their growth potential and be positively associated with birth size and, thus, the risk of breast cancer.