One hundred and thirteen women aged 70 years or more with locoregional breast cancer were treated with tamoxifen alone as primary treatment. They were followed for a minimum of 5 years. Complete response occurred in 38 women, partial response in 17, no change in 34 and progressive disease in 24. Where progressive disease occurred, or where patients relapsed after an initial response, the most suitable conventional therapy was given. The actuarial 5-year survival rate was 49.4 per cent for all patients and was much higher (92 per cent) in those showing an initial complete response. Seventy patients (61.9 per cent) were not controlled by tamoxifen alone to death or most recent follow-up. Tamoxifen provides an alternative treatment for operable breast cancer in older women in the short term and may be particularly suitable for those with concurrent disease or who are unwilling to undergo surgery. The low morbidity rate from tamoxifen must be balanced against the need to maintain close follow-up. In the medium to long term, sole primary treatment by tamoxifen delays more definitive therapy.