The controversy about the best treatment for primary breast cancer will be settled only when properly designed clinical trials are completed. Most surgeons would rather await the results of such trials than participate in them. Prominent among the reasons for this view is the belief that an adequate cancer operation can seldom be performed with appropriate cosmetic preservation of the breast and, therefore, the trial of an unproven operation is not justified, because nothing can be gained. The poor cosmetic result is often owing to lack of experience with segmental mastectomy. From experience with 400 patients in the National Surgical Adjuvant Breast Project (NSABP) protocol has emerged an appreciation of the technical points that permit adequately wide local excision with minimal cosmetic loss. The results should stimulate both patients and surgeons to consider appropriate clinical trials for primary breast cancer surgery. This paper considers the causes of cosmetic failure and suggests the means of overcoming them.