Myoclonus dystonia syndrome (MDS) refers to a group of heterogeneous nondegenerative clinical conditions characterized by the association of myoclonus and dystonia as the only or prominent symptom. The " core" of MDS is represented by inherited myoclonus-dystonia (M-D), a disorder with autosomal-dominant inheritance and reduced penetrance, beginning in early childhood with a relatively benign course, with myoclonus as the most predominant and disabling symptom. Alcohol responsiveness and psychiatric symptoms are characteristic features. Mutations in the epsilon-sarcoglycan gene (SGCE, DYT11) represent the major genetic cause, but M-D is genetically heterogeneous. In a variable proportion of M-D patients no mutation is found, and at least one other locus (DYT15) has been linked to the disease. Patients with primary dystonia, with or without the DYT1 mutation, may show irregular and arrhythmic jerky movements associated with dystonia. Usually dystonia is the prominent symptom and the myoclonic jerk involves the same body region; this condition, currently defined as " myoclonic dystonia," is included in the spectrum of MDS. Dopa-responsive dystonia due to mutation in the GTP-CH gene and vitamin E deficiency can present with a phenotype of dystonia and myoclonus in combination; both conditions should be considered in the diagnostic approach to patients since they are potentially treatable.