The incidence of breast cancer in premenopausal women is increasing and many of them still remain fertile after treatment. Allied to the current tendency to postpone pregnancy, it is expected that an increasing number of patients undergoing conservative treatment for breast cancer will get pregnant. Anatomical and histopathological aspects and the probability of lactation and breast feeding after breast irradiation are reviewed in this article. Lactation is possible after radiotherapy, present in at least 50% of the patients, but in reduced volume. This perspective is more correlated to the type of surgery and radiation dose used. Biochemical changes were observed in irradiated breast milk. Breastfeeding in the contralateral breast is not affected.