This study consisted of 3 periods: OLE Titration (12 weeks), OLE Maintenance (424 weeks), and OLE Follow-up (4 weeks). During the OLE Titration Period, participants were titrated to their maximum tolerated dose (MTD) of perampanel, up to a maximum of 12 mg/day. The OLE Maintenance Period began at completion of the OLE Titration Period; participants remained on the dose achieved at the end of the OLE Titration Period unless dose adjustment for tolerability reasons was necessary. Participants who either withdrew from the study prematurely or completed the OLE Maintenance Period returned for a final visit at the end of the 4-week OLE Follow-up Period.