The authors report the findings in 107 women who are known to have survived 25 years from among a population of 746 consecutive patients who underwent radical mastectomy for breast carcinoma at the University of Chicago Hospitals and Clinics from 1929 to 1955. Of these patients, 103 had invasive carcinomas, two had intraductal carcinomas, and two had subareolar papillomatosis. Six patients had to be excluded because of inadequate pathologic material. The pathologic findings in 93 cases were compared with those in an equal number of control cases dying within a comparatively short period (median, 3.4 years; range 0.9-9.9 years) after radical mastectomy. These were matched for age, tumor size, and number of positive nodes. Only two of our patients suffered recurrences, and none died of her original tumor; however, 12 developed second primaries in the opposite breast, and four died from them. Compared with all patients who underwent radical mastectomy in this period, the 25-year survivors were younger (69 versus 43% were younger than age 50 years), had smaller tumors (39 versus 26% less than 2 cm in diameter), and a larger number (60 versus 39%) had negative nodes. Nonetheless, 12% of the survivors had tumors larger than 5 cm in diameter and 11% had four or more positive nodes. Histologically, 19% of the 25-year survivors had medullary, mucoid, infiltrating lobular, tubular or lipid rich carcinomas, whereas there was only one lobular and one apocrine carcinoma in the control group. Compared with controls, the survivors had a higher percentage of Grade I tumors and a lower incidence of lymphatic and vascular invasion in the breast. Only one 25-year survivor compared with 16 controls had blood vessel invasion. A surprising 63% of the 25-year survivors had lymphatic or vascular invasion within the tumor, or lymph node metastases compared with 82% of controls. While our studies confirm the importance of these well-known prognostic indicators, it also shows that some patients with pathologically unfavorable lesions, i.e., large tumors of high grade with extensive lymphatic invasion and many positive nodes, treated by radical mastectomy may survive for 25 years. However, we could not accurately predict, among the cases we studied, who would be expected to survive 25 years or who would die within four years.