To evaluate the accordance of size measurements of malignant breast lesions 65 women with 76 malignant lesions were preoperatively examined with triple diagnosis (mammography was performed in three views with additional views if necessary) and dynamic MR imaging using a subtraction technique with a 3D T1-weighted sequence. Maximum lesion size at histopathology was used as gold standard and compared with maximum lesion size at MRI and mammography. All measurements were made independently for each method. Histopathology verified 48 invasive, 5 in situ, and 23 mixed lesions. No significant difference was found for the pure invasive lesions ( p=0.366). In the mixed lesions a slightly better result for MRI was indicated ( p=0.116), although there was a great spread. Only five pure in situ lesions were assessed, too few to draw any statistical conclusions ( p>0.5). An overall difference indicated a slight superiority of MRI ( p=0.097). The MR imaging and mammography are both good at measuring the size of detected invasive breast malignancies. The total sizes of mixed lesions are frequently underestimated by both MRI and mammography, although the invasive parts were equally well described and measured with both methods.