We have reviewed our experience with partial mastectomy without radiation therapy at the Cleveland Clinic during the years 1957 through 1976. Three-hundred-twenty-two patients have had partial mastectomy, 18 per cent of our entire series of 1761 patients treated for breast cancer during these years. This percentage has increased significantly in the past 10 years. Survival results after partial mastectomy are equal to or better than the other operative procedures we have employed in the treatment of primary breast cancer. But we believe these results relate to the selection of more favorable patients with small tumors for partial mastectomy rather than to a benefit of the operative procedure itself. Local recurrence rates, in our experience, are identical after partial mastectomy as compared to patients having had modified radical mastectomy or total mastectomy without axillary dissection. There is an additional incidence of new primary breast cancers occurring in the same breast treated by partial mastectomy - 7 per cent at 5 years. The presence of axillary lymph node involvement has been identified as an adverse selection factor and correlates strongly with local recurrence. Perhaps in patients who have had partial mastectomy and involved axillary lymph nodes, radiation therapy should be given prophylactically to the remaining breast tissue to prevent local recurrence.