This multi-center, open-label, single-arm study evaluating the efficacy of perampanel added to monotherapy for partial onset seizures consists of 2 periods: Titration Period (12 weeks) and Maintenance Period (24 weeks). During the Titration Period, participants will begin receiving perampanel 2 milligrams per day (mg/day) and be up-titrated in no less than 2-week intervals in increments of 2 mg up to 12 mg according to the investigator's judgment. Upon entering the Maintenance Period, participants will receive the last dose they achieved at the end of the Titration Period and will continue receiving this dose once daily for the remainder of the study.