Thyroidectomy has been used for the treatment of thyroid disease for more than 100 years. In spite of the advancement of surgical techniques, there is still a risk of laryngeal nerve injury. The risk of partial or complete injury still depends on some surgical and disease-related factors. The aim of this study is to show the partial injury and to establish these risk factors via laryngeal electromyo-graphic analysis (LEMG) in postthyroidectomy patients with normal vocal cord motion and mucosal anatomy. Patients who had undergone thyroid surgery were enrolled in this prospective study. LEMG analysis was performed to all patients with normal vocal cord mobility preoperatively and was repeated after the first and the third months of surgery. Thyroarytenoid (TA) and cricothyroid (CT) muscles were used to evaluate recurrent and external branch of superior laryngeal nerves, respectively. Four of the 32 patients had mild-to-moderate degrees of partial LEMG changes during preoperative LEMG analysis of TA and CT muscles on each side. After 3 months of surgery, there was a statistically significant worsening of LEMG findings in the right and left external branches of superior and left recurrent laryngeal nerves. Disease and surgery-related risk factors were analyzed. However, there was no significant relationship on the progression of LEMG findings according to these parameters. This is the first prospective study which supports the risk of progression of LEMG changes in patients with normal laryngoscopic examination after thyroid surgery. No reliable significant risk factor was found influencing the LEMG progression.