A Safety, Efficacy and Tolerability Trial of Pregabalin as Add-On Treatment in Pediatric and Adult Subjects With Primary Generalized Tonic-Clonic (i.e., Grand Mal) Seizures.

Inclusion Criteria: * Seizures classified as Primary Generalized Tonic Clonic Seizures * Must have at least 1 PGTC seizure in the 8 weeks prior to screening * Must have a minimum of 3 PGTC seizures during the 8-week baseline phase and at least 1 PGTC in each 4-week period of the baseline phase * Currently receiving adequate and stable dosage of 1 to 3 anti-epileptic treatments (stable within 28 days of screening) * Signed informed consent and assent if a minor * Ability to comply with daily seizure and dosing diary requirements and all study procedures Exclusion Criteria: * A current diagnosis of febrile seizures, or seizures related to an ongoing acute medical illness * Focal seizures (simple partial, complex partial, or partial becoming secondarily generalized) * Status Epilepticus within 1 year prior to screening * Lennox-Gastaut syndrome, infantile spasms, Benign Epilepsy with Centrotemporal Spikes (BECTS) and Dravet syndrome * Seizures related to drugs, alcohol, or acute medical illness * Any change in anti-epileptic treatment regimen (type of medication or dose; VNS alteration) within 28 days of the screening visit or during the baseline phase * Progressive or potentially progressive structural CNS lesion or a progressive encephalopathy. * Progressive inborn errors of metabolism.