Generalized idiopathic epilepsies starting between 12 and 18 years of age are mostly represented by juvenile myoclonic epilepsy, juvenile absence epilepsy and grand-mal on awakening. The EEG and clinical description of the seizures, the different epileptic syndromes with their therapeutics, the prognosis and the familial forms with the molecular genetic aspects are studied. The importance of the history for the positive diagnosis is emphasized, in order to display the often overlooked myoclonies occurring in the morning. Differential diagnosis concerns mostly absences which are sometimes difficult to separate from frontal seizures, and in the case of first generalized tonico-clonic seizure, partial epilepsy which needs further investigations, and the exceptional progressive myoclonic epilepsy which begins the same way, but has a totally different prognosis. Psycho-social difficulties due to epilepsy and lack of therapeutic compliance are frequent. The therapeutic results are generally good but there is a high rate of relapse after medication withdrawal.