To evaluate the results of treatment of Stage I and Stage II-T1 and T2, NO and N1-carcinoma of the breast by modified radical mastectomy with preservation of the pectoralis major muscle, the survival rates of all such patients treated by the senior author from 1965 through 1968 were compared with the survival rates of a simultaneous group of patients with similar stage disease treated by conventional radical mastectomy by the same surgeon. There were a total of 134 patients, of whom 51 had modified radical mastectomy and 83 conventional radical mastectomy. The five year survival rate for those treated by standard radical mastectomy was 81 per cent, and for those treated by modified radical mastectomy, it was 84 per cent. In patients with histologically negative axillary lymph nodes, the rates were 86 per cent following both radical mastectomy and modified radical mastectomy. Four per cent of the surviving patients after modified radical mastectomy and 7 per cent of the five year survivors after radical mastectomy had evidence of metastases at five years. Locally recurrent disease was noted in 5 per cent of those who had modified radical mastectomy and 7 per cent of those who underwent standard radical mastectomy. This analysis demonstrates that there is no significant difference in the survival and recurrence rates after conventional radical mastectomy and ,odified radical mastectomy of the Patey type. There is a high incidence of recurrence-free survival after both of these operations. Since modified radical mastectomy is less traumatic, involving less damage to muscular tissues, and is followed by significantly decreased deformity, it is advised as the treatment of choice for patients with carcinoma of the breast having no or minimal evidence of axillary node involvement. More extensive tumors adherent to the pectoral fascia or associated with multiple or large palpable axillary nodes should still be treated by conventional radical mastectomy.