Our aim was to assess the feasibility and accuracy of contrast-enhanced ultrasound (CEUS) of the breast with SonoVue microbubbles for pre-operative size measurement of invasive breast carcinomas. Seven patients diagnosed with nine invasive breast carcinomas prospectively underwent gray-scale ultrasound and CEUS of the breast according to a standardized protocol. CEUS of the breast was performed by a Philips iU22 scanner equipped with a 4-8 MHz linear array transducer. We used a single dose of 2.4 ml SonoVue as contrast agent. Breast lesion morphology was scored according to the sonographic BI-RADS lexicon criteria and classified accordingly. The greatest tumor dimensions on gray-scale ultrasound and CEUS of the breast were finally compared with the greatest histopathologic tumor sizes. Gray-scale ultrasound underestimated the histopathologic tumor size in 6/9 cases (67%), whereas CEUS of the breast underestimated tumor size in only 3/9 (33%) cases. CEUS of the breast was significantly more accurate for tumor size assessment. Greatest tumor dimension as measured with gray-scale ultrasound of the breast was within 2 mm of the pathologic tumor size in only 2/9 cases (22%), whereas CEUS of the breast accurately assessed tumor size within 2 mm of pathologic tumor size in 6/9 (67%) of the cases (P<0.05). CEUS of the breast proved to be a feasible and safe procedure. It is more accurate than gray-scale ultrasound of the breast for pre-operative size assessment of invasive ductal breast carcinomas.