Myoclonic jerks occur in a number of different syndromes. There is many classifications of myoclonus. It is preferred the Fejerman classification, slightly modified that present the following five groups: 1. Myoclonus without encephalopathy and without epilepsy, which includes physiological myoclonus; 2. Encephalopathies with non epileptic myoclonus, which includes Kinsbourne syndrome and certain types of hyperekplexia which pose differential diagnosis problems with reflex myoclonic epilepsy; 3. Progressive encephalopathies with myoclonic seizures which includes typical and atypical progressive myoclonus epilepsies; 4. Epilepsies and epileptic encephalopathies with myoclonic seizures, which includes severe epilepsies which leads to mental retardation, as Otahara syndrome, West syndrome and Lennox-Gastaut syndrome, and other epilepsies which present sometimes myoclonic seizures, as Landau-Kleffner syndrome, 5. Comprises true myoclonic epilepsies, differentiating syndromes recognized as idiopathic, -benign myoclonic epilepsy of infancy, reflex form of benign myoclonic epilepsy in infancy, eyelid myoclonic with absences, perioral myoclonic with absences and juvenile myoclonic epilepsy-, cryptogenic-severe myoclonic epilepsy of infancy, myoclonic-astatic epilepsy and epilepsy with myoclonic absences-, and symptomatic as the generalized myoclonus in children with static encephalopathies. The epileptic syndromes of the last group are described. Despite this classification, apparently clear, there is still a great deal of confusion and in clinical practice, many cases are difficult to classify.