On the basis of 597 cases of benign and malignant tumoral, respectively dysplastic diseases of the breast, operated at the IInd Surgical Clinic of Tirgu-Mureş during the period 1977-1983, the authors consider the fibrocystic disease (FCD) of the II and III degree as a facultative precancerous lesion. The extremely high frequency of FCD associated to the mammary cancer in young women, as well as of intense epithelial proliferations and intermediate forms, of transition from typical epithelial hyperplasias to the atypical forms observed in some of these cases, is pointed out. The 4 cases (1.94%) of mammary neoplasms which occurred late after a mammary sectorectomy performed for FCD illustrate that the risk of mammary neoplasm in FCD is 7.4 times higher than the mammary cancer rate in women without FCD. In the extensive forms of FCD with marked epithelial proliferations, especially if additional risk factors are also present, the authors recommend a uni- or bilateral subcutaneous mastectomy, a uni- or bilateral simple mastectomy respectively. They deem necessary the setting up, in all departments of general surgery, of an adequate organizational framework for the dispensary care, the hormonal therapy and the control of women with FCD.