Many epidemiological studies show clearly the restraining effect of breast-feeding on breast cancer. So it could be shown that breast-feeding for one year reduces the individual risk for premenopausal breast cancer by 45%. The risk of postmenopausal breast cancer in the developed countries could be decreased by 42% by increasing the breast-feeding time in life. Most authors assume that the protective value of breast-feeding is hormone-conditioned. Further theoretical implications result from the increasing knowledge of the immunologic characteristics of the mother's milk. Beside well-known positive effects of breast-feeding on children's health, breast-feeding should also be further promoted from the view of women's health.