Purpose. Brivaracetam (BRV), an antiseizure medication indicated for focal-onset seizures, has shown efficacy in the treatment of focal to bilateral tonic-clonic seizures (FBTCS). We aimed to determine the effectiveness and safety of BRV in patients with FBTCS and generalized tonic-clonic seizures (GTCS). Methods. We performed a multicenter, retrospective, longitudinal study in adult patients with epilepsy who experienced at least one FBTCS or GTCS before starting BRV (baseline visit). Data were collected from consecutive outpatient visits over a 4-year period. All patients had been followed for at least 3 months before the baseline visit and completed a minimum follow-up of 3 months after starting BRV. Response (≥50% reduction in FBTCS/GTCS frequency) and retention rates, as well as seizure freedom and presence of adverse events at 3, 6, and 12 months, were recorded as outcome measures. Results. 114 patients were included (mean age
36.3
±
18.0
years, 52% male, 36.6% genetic generalized epilepsy); 94 had a 12-month follow-up period. At 12 months’ follow-up, the response rate was 83%, and 73.4% of patients were FBTCS/GTCS-free. Retention was 79% at 12 months. Adverse events occurred in 29.8% of patients, the most common being drowsiness (14.9%). No significant differences were found in response rates between FBTCS and GTCS. Drug resistance was independently associated with lower response and seizure freedom rates at follow-up. The absence of a titration period predicted seizure freedom and response at 3 months. Conclusions. BRV is an effective and well-tolerated treatment in patients with focal to bilateral tonic-clonic seizures and generalized tonic-clonic seizures.