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Background Dravet syndrome (DS) is a rare, drug-resistant, developmental and epileptic encephalopathy characterized by frequent seizures and motor, behavioral, and cognitive impairments. Fenfluramine was evaluated in three pivotal phase 3 randomized-controlled studies ( NCT02682927, NCT02826863, NCT02926898) and is approved for the treatment of seizures associated with DS (US, EU, UK, Japan, among others) in patients ≥2 years old. The studies were pooled and stratified by baseline characteristics not originally reported.Methods Patients (2–18y) with DS were treated with placebo or fenfluramine (0.2 mg/kg/d or 0.7 mg/kg/d without stiripentol [0.2FFA, 0.7FFA], 0.4 mg/kg/d with stiripentol [0.4FFA]). Data were stratified by fenfluramine initiation age (<4y, ≥4y), severity (1–3, 4–6, and 7+ failed antiseizure medications [ASMs]), and genotype ( SCN1A+/-). Baseline characteristics, safety, median percentage change in monthly convulsive seizure frequency (MCSF), median longest interval of convulsive seizure-free days (SFDs), and Clinical Global Impression—Improvement (CGI-I) scores (caregiver/investigator) were assessed.Results Among 348 patients (0.2FFA, n=85; 0.4FFA, n=43; 0.7FFA, n=88; placebo, n=132), 83.7%-89.4% were ≥4y; 70.6%-81.4% had genotype SCN1A+. Failed ASM rates were generally high (4–6: 31.8%-48.8%; 7+: 34.8%-57.6% [no 0.4FFA-treated patients]). Treatment-emergent adverse events rates were similar across stratified groups. Fenfluramine treatment was associated with greater decrease in MCSF, increase in longest interval of SFDs, and higher CGI-I scores versus placebo, regardless of stratification.Conclusions Fenfluramine is associated with improved outcomes relative to placebo, regardless of age, severity, or genotype. Analyses of stratified groups in larger populations may provide a better understanding of the benefits seen with various DS subpopulations and synergies with concomitant medications.