BACKGROUND: Perampanel is approved for adjunctive treatment of partial seizures, with or without secondary generalised (SG) seizures, and for primary generalised tonic-clonic seizures (PGTCS) in epilepsy patients aged ≥12 years. METHODS: In open-label extension (OLEx) studies (Studies 207 [NCT00368472], 307 [NCT00735397], 335 OLEx [NCT01618695], and 332 OLEx [NCT02307578]), patients received perampanel (maximum 12 mg/day) during a blinded Conversion Period (6–16 weeks) and a Maintenance Phase (32–424 weeks [≤1 to≤8 years’ exposure]). Efficacy and safety were analysed for patients experiencing SG seizures or PGTCS. RESULTS: Mean cumulative exposure to perampanel was 102.3 weeks for patients with SG seizures (n=720) and 83.9 weeks for patients with PGTCS (n=138); median percent reductions in seizure frequency were 66.7% and 80.6%. Corresponding 50%, 75% and 100% responder rates were 59.5%, 45.3% and 18.4% for SG seizures, and 72.5%, 51.5% and 16.7% for PGTCS. For each seizure type, efficacy was observed, irrespective of prior treatment during the Double-blind Phase. Treatment-emergent adverse events (TEAEs) affected 90.3% of patients with SG seizures and 87.0% of patients with PGTC seizures. CONCLUSION: Long-term adjunctive perampanel demonstrated efficacy for SG seizures or PGTCS. Safety outcomes were consistent with the known safety profile of perampanel. Funding: Eisai Inc.