Between 1982 and 1989, 200 patients aged 70 or over seen in one Breast Unit, who were considered to have a surgically resectable cancer of the breast were prospectively randomized to primary surgery or tamoxifen 20 mg per day. At a median follow-up of 6 years (range 3-11 years) and at the censoring date there were 61 first events in the tamoxifen group. Fifty three patients developed local relapse or progression of the cancer; three patients had simultaneous local progression or relapse and distant metastases. In addition a further five patients developed distant recurrence only. In the surgical arm there were 50 events. Thirty-six patients developed local recurrence only; eight had simultaneous local and distant recurrence. A further six patients developed distant metastases of which two subsequently developed local recurrence. There were 33 deaths in the tamoxifen group and 28 deaths in the surgical group of which 17 and 15, respectively were directly attributable to breast cancer. The disease-free interval did not differ between the two groups. Following treatment with tamoxifen, at the censoring date which was the date of last clinical examination or arbitrarily, the date of death, 39 patients had no evidence of relapse whereas in the surgical arm there were 50 patients who had no evidence of recurrence. Fifty-three patients in the tamoxifen arm had local relapse only and were available for crossover to surgery, 39 accepted surgery. Eight developed further local recurrence, 10 developed distant metastases and 21 remained free of disease. Thirty-six patients in the surgical group developed local relapse only and were available for crossover to tamoxifen. Thirty one accepted treatment with tamoxifen, 14 had progression of their local recurrence, seven developed distant metastases and 10 had no further recurrence. Thus in the tamoxifen group, 39 had no progression of their disease and a further 21 benefited from subsequent surgery: 60% in all. In the surgical group 50 had no recurrence of their disease and a further 10 benefited from subsequent tamoxifen therapy: 60% in all.