In this study of 2092 women with cancer of the breast, those who had practiced breast self-examination (BSE) had earlier cancer than did those who had not practiced BSE. This was true for both black and white races, all educational and economic levels, each age group, and within each period of delay between first symptom and medical consultation. The practice of BSE increased as the educational level rose and diminished as age advanced. A higher percentage of whites than blacks used the procedure. Breast self-examination is safe and without cost to the women who practice it. It has the potential for helping more women to find their breast cancer early than any other method now available and feasible for widespread use.