The report describes a clinical trial on conservative surgery in progress at the National Cancer Institute of Milan, Italy. The randomized clinical trial compares radical mastectomy with a more conservative procedure consisting of mammary resection plus axillary dissection plus radiotherapy. The resection comprises an entire quadrant of the breast together with the overlying skin and the corresponding portion of the fascial sheet of the pectoralis major. The axillary dissection is performed in continuity with the resected breast quadrant except in cases with tumors of lower inner quadrants, who need two separate incisions. After surgery the patients receive 6000 rads to the residual breast tissue over five to six weeks, starting 15 days after operation. The cosmetic results are satisfactory in approximately 70% of cases. The trial is limited to cases with tumors less than 2 cm and no palpable axillary nodes (T1N0M0). Patients with histologically positive lymph nodes (N+) are submitted to adjuvant chemotherapy with CMF for one year. From September 1973, to October 1976, 331 cases entered the trial. One hundred sixty were treated with radical mastectomy and 164 with the conservative procedure. Axillary metastases were found in 23% of the radical and in 29% of the conservative surgery group. Four local-regional recurrences have occurred till now, two in each group. Five cases in the radical mastectomy group and one in the conservative group had distant metastases. The clinical trial will collect some 500 cases by the end of 1977 and significant preliminary results are expected to be available from 1978.