The syndrome of Isaacs-Mertens is a rare neuromuscular disease in which the motor unit is continuously active. The diagnosis is based on electrophysiological methods and pharmacological tests. The involvement of laryngeal muscles observed in the reported female patient has been as yet rarely described in this syndrome. In the treatment long-term administration of carbamazepine 600 mg daily gave a considerable clinical improvement. The pathological mechanism of the syndrome is discussed in the light of the performed examinations and a review of the pertinent literature.