Breast cancer is rare before age 40. Sixty to seventy percent of breast cancers in this age group express estrogen or progesterone receptors. All following considerations refer to endocrine responsive disease. Ovarian ablation reduces the relative risk of recurrence and death by at least one quarter in the absence of chemotherapy. Chemotherapy induced amenorrhea reduces the risk of recurrence and death when compared to patients with continuing menses. Chemotherapy is insufficient therapy for very young patients with hormone responsive disease, particularly if chemotherapy fails to induce amenorrhea. Tamoxifen is effective in young patients even in combination with chemotherapy. The ablation or suppression of ovarian function was equivalent to chemotherapy in at least eight randomized trials. Preliminary evidence is compatible with an additional adjuvant effect of LHRH agonists after chemotherapy, particularly in women < 40 years of age. Young patients with endocrine responsive tumors should be treated on a clinical trial. If this is impossible, they should receive tamoxifen and either an LHRH agonist or chemotherapy or both.