The long-term disease free survival in patients treated by breast conserving therapy is similar to that of patients treated by mastectomy. In breast conserving therapy there is a significant risk of local recurrence. Although local recurrence does not appear to effect survival, there is certainly associated morbidity and attendant emotional trauma. Microscopic evaluation of the margins of lumpectomy specimens is the only way to define the extent of the tumour and the adequacy of resection. We intended to check the influence of standardized handling instructions for pathological examination on the results of histological margin assessment. These instructions are part of a practice protocol for all branches involved in BCT. We compared the results of our standardized margin investigation of 100 cases with the analysis of the margin status of 100 Lumpectomy specimens each from two other periods of time with different handling. Before 1989 only margins where tumor tissue was suspected when checked with the naked eye were investigated microscopically. From 1990 till 1991, margins were evaluated more intensively, but the evaluations were not standardized and did not consider the orientation of the ductal system, which was the base of examination after 1992. In 28% of cases, tumour tissue was found upon the investigation under the microscope, in the margins of lumpectomies where the margins looked clear to the naked eye. In the other periods tumour could be found in the margins in only 2% respectively 12%. Our results verify a strong influence of our practice protocol on the results of the examination of LE specimens: At first there is a higher sensitivity for tumor bearing margins compared with random sampling of margin tissue. Moreover, based on the consideration of the ductal orientation our protocol offers a better chance to detect in situ components of tumor in the margins. Finally with our method we are able to design exactly the tumor bearing margin and therefore we could take part in quality assurance of BCT.