To study the role of radiotherapy and tamoxifen after breast-conserving surgery (BCS) in patients with a favourable prognosis, a clinical trial was initiated by the German Breast Cancer Study Group (GBSG-V). Between 1991 and 1998, 361 patients (pT 1pN0M0, aged 45-75 years, receptor positive, grades I and II) were randomised to radiotherapy (yes/no) and tamoxifen for 2 years (yes/no) in a 2 x 2-factorial design; the exclusion of seven centres (14 patients) left 347 patients for the analysis. First results after a median follow-up of 5.9 years were published. Herein we present updated results after a median follow-up of about 10 years. Hundred and eleven events concerning event-free survival (EFS) have been observed. Since a strong interactive effect between radiotherapy and tamoxifen has been established, the results are presented in terms of the treatment effects for all four treatment groups separately. Mainly due to the presence of local recurrences, the event rate was much higher in the group with BCS only than in the other three groups. No significant difference could be established between the four treatment groups for distant disease-free survival rates (DDFS). Updated results give further evidence that even in patients with a favourable prognosis, the avoidance of radiotherapy and tamoxifen after BCS increases the rate of local recurrences substantially. Rates are about three times higher in the BCS only group. For the two outcomes EFS and DDFS, no important difference could be seen between the three groups with an additional treatment. However, because of the limited sample size with corresponding low power the strength of evidence for such a comparison is weak.