Objective: To evaluate the diagnostic accuracy of sentinel lymph node biopsy after neoadjuvant chemotherapy. Materials and methods: The study included 264 patients with early (operable) and locally advanced breast cancer (cTlNl-3, CT2N0-3, CT3N0-3, cT4N0-3). All patient underwent core-biopsy with histological examination and ICH (to determine the tumor grade (G), expression of ER, PR, Ki67, Her2), fine needle aspiration of suspicious axillary lymph nodes. Before, during and after the neoadjuvant therapy, all patients undergo: Physical examination (palpation), mammography, ultrasound, SPECT-CT. The effect of neoadjuvant chemotherapy was evaluated after the 2nd, 4th, and 6th cycles of therapy. 197 patients (74.6%) had tumors more than 2 cm (cT2), 210 (79.8%) were N + (cNl-N3), 174 patients (65.9%) had luminal tumors (ER+), 84 patients (31.8%) had triple-negative breast cancer (ER-, PR-, HER2-) and 53 patients (20%) had HER2-positive breast cancer. Most patients (56.4%) had a high level (> 30%) of Ki67 expression. Results: 210 of 263 patients (79.8%) had metastases in regional lymph nodes before treatment. Almost half of them had a decrease in the stage from N + to ycNO after NACT. According to the ultrasound data 48 patients had decreasing of the stage to ycNO. Sentinel lymph node biopsy showed ypNO category in 35 patients and ypN+ in 13 patients. The false-negative rate was 5.7%. The sensitivity of the method was 94.3%, the accuracy of ultrasound was 95.8%. According to the SPET-CT data 51 patients had decreasing of the stage to ycNO. Sentinel lymph node biopsy showed ypNO category in 35 patients and ypN+ in 16 patients. The false-negative rate was 2.85%. The sensitivity of SLNB after NACT in patients cN0/cN+-> ycNO was 91.2%, accuracy-96.3%, predictive value of the negative result-92.4%. Conclusion: SLNB can be performed in cN0/cN+-∗ ycNO patients after NACT, provided that 3 or more sentinel lymph nodes are removed and there are no tumor cells in them.