[Epidemiology of primary dystonia].

Introduction: Dystonia is the most difficult disorder of movement to recognize, and in which errors of diagnosis most often occur.

Development: We review the classification of the dystonias and the most important features of the different subdivisions. With regard to epidemiology, the exact incidence and prevalence of primary dystonia are not known. Figures vary considerably depending on the source, method of study and ethnic group of the population studied. In Europe the only study made of focal dystonias was carried out in Segovia, where the prevalence was about 300 persons per million. Finally we discuss some recent genetic findings related to the dystonias, which should stimulate more detailed studies to clarify the genetic basis of focal dystonias.