Between 1977 and 1983 100 elderly women (median 76.3 years) with breast cancer were treated with tamoxifen as primary therapy. The median follow-up is 59 months. Sixty-eight responded (40 CR and 28 PR) with median response durations of 47 months and 26 months respectively. Twenty-two patients had disease stabilization for a median of 15.5 months and 10 had progressive disease. The median time to best response was 13.5 weeks for patients achieving CR and 14 weeks for those with PR. Oestrogen receptor values were obtained in 37 patients of which two patients had no ER detectable. Sixty-seven per cent of ER-unknown patients responded compared with 74% of ER-rich. Likelihood of response did not appear to depend upon T-stage or age. Survival was better than that of an unmatched historical group treated with surgery/radiotherapy and compares favourably with recent reports. Although 35% have died of breast cancer, 25% died of other causes and 22% remained free of recurrence at the time of reporting or at death. Only 11% underwent subsequent mastectomy/lumpectomy and the most frequent subsequent treatments were radiotherapy to the breast (32%) and further hormonal therapies (40%). Tamoxifen is a practical primary therapy of breast cancer in elderly and frail women obviating the need for surgery in a high proportion of cases.