The authors report a case of Isaacs syndrome observed in a 40 years old woman. The clinical picture included progressive muscular weakness, dysphagia, dysphonia, dyspnea and increased perspiration. Fasciculations, facial myokymia and pseudomyotonia were observed on physical examination. Electromyographic study at rest revealed continuous electrical muscle activity. Muscle histochemistry showed type II fibers atrophy and an ultrastructural study of the gastrocnemius muscle disclosed marked cysternal dilatation of the sarcoplasmatic reticulum. An excellent clinical response was observed with the use of carbamazepine. Some recent aspects of this rare syndrome are reviewed and discussed.