Routine use of intraoperative neuromonitoring (IONM) in thyroid cancer surgery is controversial. We aimed to investigate whether it improves the completeness of thyroidectomy and ensures safety. This retrospective study included 380 thyroid cancer patients who underwent thyroidectomy, by one surgeon, between July 2006 and November 2015. Patients were grouped according to the surgeon's adaptation of IONM, as follows: none (period 1; n = 92), early (period 2; n = 141), and late (period 3; n = 147). The operative time and rates of vocal cord palsy were determined. Surgical completeness was assessed by technetium-99m imaging of the thyroid remnant and serum thyroglobulin measurement before ablation. The rate of recurrent laryngeal nerve (RLN) palsy showed a decreasing trend over time. No permanent RLN palsies occurred in nerves not invaded by tumor after routine IONM was introduced. Technetium-99m uptake (periods 1-3, 0.62 vs 0.32 vs 0.20; P < 0.01) and thyroglobulin levels (periods 1 and 2, 37.93 vs 8.98 ng/mL, respectively; P = 0.034; period 3, 9.10 ng/mL) progressively decreased. The mean thyroglobulin level dropped significantly after introduction of routine IONM. We conclude that routine IONM during thyroid cancer surgery improves surgical completeness and might prevent permanent RLN palsy over time.