The aim of the study is to evaluate the efficiency and safety of intraoperative neuromonitoring (IONM) of accessory nerves during lateral lymphodissection (LLD). Materials and Methods. Main group consisted of 63 patients with thyroid cancer (TC) with confirmed metastatic spread into cervical lymph nodes of II-V groups, and which underwent IONM of accessory nerve during LLD. Control group consisted of 60 patients in which no IONM was performed during LLD. Main group consisted of 21 males (33.3%); 42 females (66.7%): mean age 50.7 ± 8,7. Control group consisted of 11 males (18.2%); 49 females (81.8%); mean age 47.2 ± 6,8. Results. All patients of main group responded to electric stimulation of accessory nerve during IONM. 58 (92.1%) patients did not present new symptom, whereas 4 (6.3%) noted a moderate pain while lifting and stretching the upper extremity during two weeks. In 1 (1.6%) — temporary difficulty in arm abduction up to 90° was observed. In control group, in 5 (8.3%) — damage to accessory nerve was found which manifested as lack of contraction of trapezius muscle in response to electric stimulus. In 12 (20%) — pain during lifting and abduction of upper extremity on respective side was observed up to 3-4 weeks after surgery. Conclusions. IONM of accessory nerve is a safe and effective way to reduce probability of accessory nerve damage, which, together with improvement in organ-preserving techniques, is demonstrated by decrease of functional loss in upper extremities from 13.3% to 1.6% during the period from 2000 to 2020.