In the Departments of Gynaecology and of Gynaecological Radiology of the University of Heidelberg, breast conserving therapy was carried out in 1330 patients with breast cancer between 1975 and 1990. The tumour size was up to 3 cm and 28% showed positive nodes. The median age was 47.6 years, segmental resection was the standard operation and whole breast irradiation with 50 Gy and an additional boost of 10 Gy was the standard irradiation schedule. After 5 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%. 5 out of 36 of the cases of mortality died without having had a recurrence. Significant factors for local failure were following: 1. lymphangiosis of more than 1 cm in size around the tumour (p = 0.03) 2. intra-ductal non-invasive cancer of more than 1 cm in size around the primary tumour (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 tumour), tumour beyond the margins--so-called residuals, showed in 19% histologically. In the other 3 quadrants, additional secondary primaries in 25% (multicentric cancers) of macroscopical size could be confirmed in an additional study. In case of high risk for local failure, more radical surgery as well as more intense irradiation is recommended.