Between August 1989 and September 1999, breast-conservation treatment (BCT) was performed in 250 of 256 breast cancer patients. Five of the 250 patients had bilateral breast cancer, and 4 with synchronous bilateral breast cancer of the 5 were concomitantly treated by chemo-endocrine therapy before simultaneous breast-conservation surgery for bilateral breast cancer. Chemotherapy was performed using cyclophosphamide, pirarubicin, and 5-fluorouracil, while endocrine therapy was performed using an antiestrogen agent (tamoxifen or toremifene). All patients were also treated by radiotherapy. Since no severe side effects or complications were induced by these therapeutic approaches, bilateral breast cancer may be successfully treated by BCT as in unilateral breast cancer. However, of the 5 patients with bilateral breast cancer, cancer recurrence in the axillary lymph nodes was detected only in 1 patient with T2N1 cancer 78 months after simultaneous breast-conservation surgery for bilateral breast cancer.