The significance of ABO blood system groups antigens in development of some malignant tumors is already established. The alteration of hormonal homeostasis must also be taken into account. Hence the aim of the investigation was to study ABO and Rh blood system antigens and hormonal status among reproductive age women with benign and malignant breast tumors. Methods: The determination of hormones was made by the enzymatic analysis method (ELAIZA), provided by proper ELAIZA kits. For the study of ABO and RhHr system antigens, internationally recognized immunoserology methods were used. Results: High index of the breast gland tumors were revealed in patients with A(II) phenotypic group, according to the ABO system. The frequency distribution of O(I) phenotypic group was low among women with breast tumors. Among D, C, E, c and e antigens of the Rh system, the frequency of D and E antigens were increased in benign and malignant breast tumors patients. The study of hormonal balance revealed thyroid gland hypofunction and increased level of estradiol on the background of increased testosterone and decreased progesterone levels. Such hormonal imbalance and excess production of estradiol creates conditions for malignant tumor formation in reproductive age women. Conclusion: The highest frequency of breast cancer in reproductive age was revealed in A(II) group patients. The wide spectrum of hormonal disorders were revealed in breast tumor patients of the reproductive age, which was especially clear in cases of malignant tumor., Irina Nakashidze, Nanuli Kotrikadze, Anzor Diasamidze, Marina Nagervadze, Manana Alibegashvili, Liana Ramishvili, Manana Gordeziani, and Literatura