From 1973 to 1980, 701 women with small breast cancer (less than 2 cm in diameter) were randomized into two different treatments. 349 patients received classic Halsted mastectomy and 352 patients received quadrantectomy, axillary dissection and radiotherapy on the ipsilateral breast. 24.6% of the patients in the mastectomy group and 27.0% of the patients in the conservation group had axillary metastases. Overall 10 year survival was 76% in the Halsted patients and 79% in the quadrantectomy patients; 13 year survival was 69% and 71%, respectively. No differences were observed after analysis by site and size of the primary tumour and age of the patients. Patients with positive axillary nodes had consistently better survival curves in the quadrantectomy group compared with the Halsted group (not significant). Among the quadrantectomy patients there were 11 local recurrences (with 4 deaths) while among the Halsted patients, 7 had local recurrences (5 deaths). There were 19 cases of contralateral breast carcinomas in the quadrantectomy group and 20 in the Halsted group. At 16 years from the beginning of the trial no evidence of oncogenic radiation risk was observed. In patients with small size carcinomas total mastectomy should have no role.