The main purpose of the present study was to show the frequency of carcinoma, as well as proliferative epithelial lesions in 207 patients submitted to large biopsies (upper outer quadrant ressection or subcutaneous mastectomy) of the contralateral breast, without clinical and/or radiological alterations, taken simultaneously with the surgical treatment of the ipsilateral breast carcinoma We Found an incidence of 6,8% of carcinomas, 5,3% of atypical hyperplasias, 51,2% of proliferative epithelial lesions without atypia and 36,7% of non-proliferative alterations in the contralateral breast The presence of contralateral cancer was significantly related to the ipsilateral lobular carcinoma, as well as with the multifocal ipsilateral in situ carcinoma, mainly the lobular type Finally, we demonstrated that the presence of contralateral proliferative epithelial lesions showed a direct correlation to the same ipsilateral alterations.