In a group of 365 patients undergoing thyroidectomy, the group of 21 patients with invasive thyroid malignancy was compared with 344 patients with benign thyroid disease or noninvasive cancers. It was shown that the method of indirect laryngoscopic examination was a simple and efficient method for detection of vocal cord paralysis and for the assessment of involvement of the surrounding tissues by the tumor. For the preoperative diagnosis of invasion of the recurrent nerve area such criteria as changed voice, results of CT and MRT were shown to be insufficiently reliable.