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.