In this report, the results of the first controlled clinical trial on breast cancer in Germany, begun in 1983, are presented after a median follow-up of 8 years. Four-year results have been previously published. In pT1 N0 M0 breast cancer, mastectomy as the standard treatment was to be compared with tumorectomy plus radiotherapy to the remaining breast tissue. The study design, originally planned as a comprehensive cohort study including randomised and non-randomised patients, had to be changed into a prospective observation study due to the low randomisation rate. 1036 out of 1119 recruited patients were evaluable. After a median follow-up of 97 months, 237 events (local recurrence, regional recurrence, distant metastases, contralateral breast cancer or death of the patient without previous recurrence) occurred. With the exception of death without recurrence, the events were evenly distributed among the two treatment groups. The 8-year local recurrence rate of the whole patient population is 8.8%. Out of all prognostic factors examined, only tumour size and grade had a significant influence on recurrent disease. Event-free survival decreased in cases with 'uncertain' tumour margins, whereas the width of the margin has no influence on disease recurrence. Based on 151 deaths observed so far, there was no significant difference in overall survival between the two treatment groups. The 8-year results of this study are in accordance with the 4-year results reported previously and with those of other breast-conserving treatment trials. There was no significant difference between the two treatment groups with regard to event-free and overall survival. Incomplete tumorectomy had a negative influence on recurrence.