This study will assess the efficacy, safety, and tolerability of adjunctive treatment with LEV (3,000 mg/day or a target dose of 60 mg/kg/day in children) compared to placebo in reducing PGTC seizures in subjects (4 - 65 years) suffering from idiopathic generalized epilepsy uncontrolled despite treatment with one or two concomitant AEDs.

Inclusion Criteria:

• Subject with a confirmed diagnosis consistent with idiopathic generalized epilepsy experiencing primary generalized tonic-clonic seizures (IIE) that are classifiable according to the ILAE Classification of Epileptic Seizures.
• Presence of at least 3 PGTC seizures during the 8-week combined Baseline period.
• Absence of brain lesion documented on a CT scan or MRI.
• An EEG performed within 1 year of Visit 1 with features consistent with PGTC seizures or generalized idiopathic epilepsy.
• Male/female subject, >=4 or <=65 years of age at Visit 1.
• Subject on a stable dose of one or two AEDs during baseline.

Exclusion Criteria:

• Previous exposure to levetiracetam.
• History of partial seizures.
• History of convulsive or non-convulsive status epilepticus while taking concomitant AEDs within three months prior to Visit 1.