A method for electrophysiological monitoring of the recurrent laryngeal nerve during thyroid surgery is described. An electromyographic record from the muscles of the vocal folds is obtained using two fine needle electrodes. The electrodes are placed endoscopically. The nerve is identified by electrical stimulation, and the electromyographic activity is registered using a Nerve Integrity Monitor NIM-2 (Xomed-Treace). Our experience with this method in 43 patients is described. The safety of the integrity of the recurrent laryngeal nerve is increased using intraoperative monitoring. This has led to a modification of the operative concept in thyroid surgery. Electrophysiological monitoring is mandatory in surgery of large goitres, retrotracheal and substernal extension, for re-operations and malignant diseases of the thyroid gland.