Objective <p>Recurrent laryngeal nerve (RLN) injury during thyroid surgery is a major cause of postoperative voice dysfunction, particularly in patients with preoperative unilateral vocal cord paralysis (UVCP). This study aimed to evaluate the therapeutic efficacy and safety of immediate ansa cervicalis nerve (ACN)-RLN anastomosis in differentiated thyroid cancer (DTC) surgery, focusing on voice function recovery and procedural impact on oncological outcomes.</p> Methods <p>A retrospective study analyzed 80 patients with DTC who underwent thyroidectomy between Sept 2017 and Jan 2022. Twenty with RLN invasion received immediate ACN-RLN anastomosis: Group A (UVCP, <i>n</i> = 5) and Group B (normal, <i>n</i> = 15). Sixty without RLN invasion served as controls: Group C (postoperative hoarseness, <i>n</i> = 30) and Group D (no hoarseness, <i>n</i> = 30). Voice outcomes were assessed by videostroboscopy, acoustic parameters (noise-to-harmonics ratio [NHR], jitter, shimmer, maximum phonation time [MPT]), Grade-Roughness-Breathiness (GRB) scale, and Voice Handicap Index-10 (VHI-10) at baseline, 1, and 6 months postoperatively.</p> Results <p>ACN-RLN anastomosis demonstrated excellent intraoperative safety without increasing blood loss, drainage, or hospital stay. Patients with preoperative UVCP showed significant voice deterioration at 1 month but achieved near-baseline recovery by 6 months. Intervention groups exhibited transient voice impairment compared to controls, with complete recovery by 6 months. Stable voice parameters were maintained in patients without preoperative vocal dysfunction.</p> Conclusions <p>Immediate ACN-RLN anastomosis is a safe and effective strategy for voice function restoration following RLN resection in thyroid cancer surgery, particularly benefiting patients with preoperative UVCP without compromising oncologic radicality.</p> Graphical abstract <p>Schematic diagram comparing the recovery of voice function and safety assessment of ACN-RLN anastomosis</p> <p></p>