PURPOSE: This study aims to evaluate the sensibility and specificity of MRI in the detection and size measuring of residual breast cancer in patients treated with neoadjuvant chemotherapy before surgery. PATIENTS AND METHODS: This is a retrospective study of 32 women, who underwent breast MRI before and after neoadjuvant treatment. MRI has been confronted to surgical pathology results. RESULTS: The sensibility of MRI to assess pathologic Complete Response (no invasive residual tumor) was excellent (100%) but the specificity was low (55,5%). There was no false negative case and four false positive cases (Two ductal carcinomas in situ and two scars-like fibrosis). When MRI outcomes were compared with the presence or absence of invasive or in situ residual carcinoma, only one false negative case was noticed (one "in situ" residual tumor). The correlation between tumor size measured by MRI and histopathology was low (r=0,32). Underestimations of tumor size were due to non-continuous tumor regression or invasive lobular carcinoma or association of invasive carcinoma and intra ductal breast cancer. Over estimations of tumor size were due to chemotherapy-induced changes. CONCLUSION: MRI is a sensitive but poorly specific method to assess the pathological complete response after neoadjuvant chemotherapy. Estimation of tumor size and detection of isolated residual in situ carcinoma are fare. Therefore, surgical intervention remains necessary whatever the MRI outcomes.