Tamoxifen (TAM) treatment following isolated locoregional recurrence of breast cancer significantly increases 5-year disease-free survival rates compared with observation alone in potentially hormone-responsive patients [J Clin Oncol 1994, 12, 2071-2077]. The treatment outcome was re-analysed by menopausal status (stratification factor) in 35 premenopausal and in 132 postmenopausal patients. Disease progression was highly reduced by tamoxifen in the postmenopausal group and was similar to control in the premenopausal group. However, the 5-year cumulative incidence analysis of the type of first failure showed TAM to be associated with increased incidence of distant metastases (P = 0.01) in premenopausal patients. TAM reduced local progression (P = 0.40) in premenopausal and both types of failure (P = 0.16 and P = 0.001, respectively) in postmenopausal patients. Administration of TAM was associated with a decrease of 5-year overall survival from 90 +/- 7% to 60 +/- 14% in premenopausal patients. Although cautious interpretation of these results is highly recommended due to the small patient numbers and the retrospective subset analyses, these findings might be worthy of further investigation in larger trials. Prospective randomised studies to test hormonal treatment outcome by menopausal status should be encouraged in breast cancer.