The study was carried out to evaluate the response to preoperative chemotherapy of locally advanced breast cancer with MRI. The series included 45 women with locally advanced breast cancer who underwent MRI before and after neoadjuvant chemotherapy. Based on the volume of residual disease, the response to chemotherapy was classified as: complete response, partial response, minor response, no change and disease progression. Responses to neoadjuvant chemotherapy were compared to MRI findings and to prognostic factors. Based on MRI findings 8 patients were assigned to the complete response group, 16 to the partial response group, 11 to the minor response group, 9 to the no change group and 1 patient to the disease progression group. MRI showed 90.2% sensitivity, 100% specificity and 91.1% accuracy. The correlation between MRI findings and prognostic factors may be useful to predict cancer aggressiveness and to understand the natural history of different breast carcinomas.