Background. Comprehensive treatment of breast cancer includes surgery, radiation therapy and systemic treatment. Radiation therapy plays an integral role in the treatment of early breast cancer. The appointment of a targeted dose of radiation to the bed of the primary tumor reduces the risk of local recurrence.Objective: to evaluate the effectiveness of intraoperative radiation therapy in the treatment of early breast cancer.Materials and methods. A retrospective study was conducted on the basis of the St. Petersburg City Clinical Oncology Center. Patients with organ-preserving surgery and intraoperative radiation therapy were selected. Of the 352 patients, 273 patients met the inclusion/non-inclusion criteria. Inclusion criteria were verified breast cancer, clinical stage I–IIA, tumor size no more than 3 cm, absence of visible axillary lymph nodes and monocentric nature of tumor growth. All patients underwent sectoral resection of the mammary gland with a biopsy of the sentinel lymph nodes and intraoperative radiation therapy.Results. The mean age of the patients was 59 years. For 273 patients, the median follow-up was 59.1 months. During this period, 18 (6.6 %) local recurrences of the disease were noted, of which 7 (39 %) patients with luminal A, 6 (33 %) patients with luminal B, 1 (6 %) patient with luminal B HER2/neu 3+, and 4 (22 %) patients with triple negative breast cancer. Within 3 years of follow-up, recurrence-free survival was 98.5 %, within 5 years – 96.4 %.Conclusion. The use of intraoperative radiation therapy for early breast cancer is an effective and safe treatment method.