The paper summarizes data on the epidemiology and clinical polymorphism of the major types of myotonias. Presents both familial and sporadic cases of myotonia congenita, atrophica, dystrophica, and Eulenburg's [correction of Eilenburg's] paramyotonias. Describes the clinical picture of Thomsen's disease in childhood. Discusses the types of disease inheritance and nosological entities of myotonias. The material has been obtained from the studies performed over 25 years, which allows the course of the disease to be followed up in families and in individuals, and enables the patients' migration in the region and outside to be traced.