In 6307 cervicotomies for thyroid and parathyroid excision, 33 cases of nonrecurrent inferior laryngeal nerve were identified (0.52%). The anomaly was observed in 31 cases from 4921 dissections on the right side (0.63%) and in two cases from 4673 dissections on the left side (0.04%). Of the 31 patients who were initially seen with this anomaly on the right side, no innominate (brachiocephalic) artery was found; the right common carotid artery was arising directly from the aortic arch. The aberrant subclavian artery could always be felt against the vertebral column behind the esophagus. The two patients with the anomaly on the left side had a right aortic arch associated with situs inversus viscerum. In one case of invasive thyroid carcinoma, the nerve had to be sacrificed. In all of the other patients, postoperative laryngoscopic findings were normal. The nervous anomaly was of vascular anomaly origin in all cases. Predisposing factors for its onset during aortic arch development are discussed. Before surgical treatment, the diagnosis may only be made if vascular anomaly is suspected. Impairment of swallowing is the only clinical symptom to be looked for. The retroesophageal subclavian artery may be detected on chest x-ray films (20%) or by the compression and distortion of the esophagus shown during barium swallow tests (97%). Although rare on the right side and exceptional on the left, an aberrant nonrecurrent pathway for the inferior laryngeal nerve represents a major surgical risk. This is an additional argument in favor of systematic dissection of the inferior laryngeal nerve during thyroid or parathyroid excision.