Aims: Pre-operatively, to exclude multiple invasive tumours not discovered by mammography and sonography: in patients referred for breast conservation surgery. Methods: A supplementary MR-mammography was offered to all patients with mammographic and/or sonographic ascertained rumours less than 2 Cm in diameter. Results: Forty patients were offered this additional examination. In accordance with the MR diagnosis, 51% of the planned surgical procedures were changed, Nine patients had more than one invasive tumour, and in four patients the tumour was >2 cm in diameter. One patient had no tumour at all, and in four patients the MR-mammography suggested benign fibroadenomas, which resulted in small excisions. One patient with a suspect MR-mammography presented sclerosing adenosis at surgery. Three patients had to be excluded due to MR problems. Ten patients preferred mastectomy, although the MR-mammography had shown only a single invasive tumour. Conclusion: MR-mammography is recommended as a pre-surgical diagnostic procedure in patients allocated to breast conservation surgery.