Conservation surgery and irradiation were compared with radical or modified radical mastectomy, without irradiation, in the treatment of clinically favorable breast cancer. Patients with minimal breast cancer, stage I (T1 N0), and stage II (T1 N1, T2 N0, or T2 N1) were found to have similar five- and ten-year survival rates for the two types of primary treatment. Local recurrence rates were also similar: 0.8%, 4.4% and 8.4% for radical mastectomy, and 2.5%, 6.8%, and 4.9% for conservation surgery and irradiation, respectively, in each successive stage of disease. Cosmetic and functional results were deemed satisfactory and supported consideration and examination of this alternative to radical mastectomy for selected patients with early breast cancer.