Inclusion Criteria:

• Subjects with a confirmed diagnosis consistent with idiopathic generalized epilepsy experiencing myoclonic seizures (IIB) that are classifiable according to the International Classification of Epileptic Seizures. To ensure an idiopathic generalized epilepsy population, only these subjects with the diagnosis of juvenile myoclonic epilepsy (JME), juvenile absence epilepsy (JAE) or epilepsy with generalized tonic- clonic seizures on awakening must be included.
• Presence of at least eight days with at least one myoclonic seizure (IIB) per day during the eight weeks of the Baseline period.
• Absence of brain lesion documented on a CT scan or MRI; if a CT scan or MRI has not been performed within the past five years before Visit 1, a CT scan (or MRI where legally required) should be performed during the Baseline period.
• Presence of EEG features consistent with idiopathic generalized epilepsy on an EEG recorded during the Baseline period or no more than one year before Visit 1.
• Male/female children ≥ 12 years of age or adult ≤ 65 years of age at Visit 1.
• Subject on a stable dose of one standard anti-epileptic treatment for at least four weeks before Visit 1.

Exclusion Criteria:

• Previous exposure to levetiracetam.
• History of partial seizures.
• History of convulsive or non-convulsive status epilepticus within 3 months prior to Visit 1.
• Subject taking vigabatrin or tiagabine, subject on felbamate with less than 18 months exposure, and subject under vagal nerve stimulation or ketogenic diet.
• Subject taking any drug (except the concomitant AEDs) with possible CNS effects.