In the Department for Gynecology and the Department for Gynecologic Radiology, University of Heidelberg, breast conserving therapy was carried out in 1,330 patients with breast cancer between 1975 and 1990. The tumor size was up to 3 cm, 28% showed positive nodes. The medium age was 47.6 years, segmental resection was the standard operation, whole breast irradiation with 50 Gy and an additional boost of 10 Gy was standard irradiation schedule. After five years (n = 307) the following results were observed: local failure 6.8%, regional lymph node recurrence 2.1%, overall survival 88.3%, disease-free survival 81.2%. Five out of 36 of the death-cases died without recurrence. Significant factors for local failure were following: 1. lymphangiosis of more than 1 cm in size around the tumor (p = 0.03); 2. intra-ductal non-invasive cancer of more than 1 cm in size around the primary (p = 0.01); 3. intra-ductal non-invasive cancer reaches the margin of resection (p less than 0.00001). With segmental resection (2 cm margin macroscopically free of tumor) showed in 19% histologically tumor beyond the margins so-called residuals. In the other three quadrants additional second primaries of (multicentric cancers) macroscopical size could be confirmed in an additional study. In case of high risk for local failure more radicality in operation as well as in irradiation is recommended.