In a multicenter trial of adjuvant therapy in stage II breast cancer, 719 postmenopausal patients were randomized to one of three treatment regimens: radiotherapy only or in combination with adjuvant tamoxifen for one year, or adjuvant tamoxifen without radiotherapy. At twelve years of follow-up (median 9 years), no statistically significant differences in survival or recurrence-free survival were observed. However, the rate of loco-regional recurrency was lower among patients treated with both radiotherapy and tamoxifen. The rate of bilateral breast cancer was reduced in tamoxifen-treated patients whereas the rate of new primary malignancies other than breast cancer was somewhat higher in tamoxifen-treated patients. Adjuvant therapy in breast cancer may influence not only breast cancer recurrences and mortality but also later disease patterns and cause-specific mortality.