From 1973 to 1980, we carried out a controlled study at the National Cancer Institute in Milan to consider the value of a conservative procedure in patients with breast cancer of small size. We randomized 701 patients with breast cancer measuring less than 2 cm in diameter and with no palpable axillary lymph nodes to Halsted radical mastectomy or to "quadrantectomy" with axillary dissection and radiotherapy to the ipsilateral residual breast tissue. We treated 349 patients with Halsted mastectomy and 352 with quadrantectomy. The two groups were comparable in age distribution, size and site of primary tumor, menopausal status, and frequency of axillary metastases. There were three local recurrences in the Halsted group and one in the quadrantectomy group. Actuarial curves showed no difference between the two groups in disease-free or overall survival. From these results, mastectomy appears to involve unnecessary mutilation in patients with breast cancer of less than 2 cm and no palpable axillary nodes.