From 1973 to 1980 we randomly assigned 701 patients with breast cancer measuring less than 2 cm in diameter and with no palpable axillary lymph nodes to Halsted radical mastectomy (n 349) or to 'quadrantectomy' with axillary dissection and radiotherapy to the ipsilateral breast tissue (n 352). The two groups were comparable in age distribution, size and site of primary tumor, menopausal status, and frequency of axillary metastases. The average follow-up time was 103 months. Actuarial curves show no difference between the two groups in the disease-free interval after surgery or in the overall survival rate. At 8 yr the disease-free survival was 77% for the patients in the Halsted group and 80% for those in the 'quadrantectomy' group, and the overall survival was 83 and 85% respectively. We conclude that small breast cancers may be safely treated with the conservative treatment described. In our opinion total ablative operations are not justified.