The aim of the present trial was to investigate the protective effects on ovarian function, and the efficacy and tolerability of goserelin added to adjuvant chemotherapy for early breast cancer. Following surgical treatment, 64 premenopausal patients with early breast cancer received goserelin 3.6 mg (every 28 days for 1 year) and an adjuvant treatment which was chosen according to the patient's prognosis. Median age was 42 years (range 27–50). ECOG performance status was 0–1 in all patients. Twenty-eight patients (44%) had estrogen receptor (ER)+ tumors and 36 (56%) patients had ER– tumors. Fifty-two (81%) patients had stage II disease and 12 (19%) had stage III disease. Eighteen patients received cyclophosphamide, methotrexate and 5-fluorouracil chemotherapy, 46 patients received an anthracycline-based regimen, and nine of them received high-dose chemotherapy and autologous peripheral blood progenitor cell transplantation. Fifty-one patients (80%) were irradiated. ER+ patients also received tamoxifen for 5 years. Serum estradiol was suppressed to values below 40 pg/ml in all patients. After a median follow-up of 55 months, 86% of patients had resumed normal menses, 84% of patients were disease-free and 94% were alive. The 1-, 3- and 5-year projected recurrence-free survival rates were 100, 81 and 75%, respectively. Five years after treatment one patient had a pregnancy that ended with a normal childbirth. No unexpected adverse events were reported. These data show that the addition of goserelin to adjuvant therapy of premenopausal patients with early breast cancer is well tolerated and protects long-term ovarian function.