Dravet syndrome (DS) is an epileptic encephalopathy mostly due to haploinsufficiency of theSCN1Avoltage-gated sodium channel subunit. Disease presentation (i.e., severe seizures and early life mortality) is highly recapitulated in mice haploinsufficient inScn1a(Scn1a+/-). However, phenotypic characterization inScn1a+/-mice in a sex and temporal manner is limited. Given the reliance of mouse models for studying disease pathophysiology and for the development of novel treatments, we tested whether mortality and seizure morbidity differed among young and adult male and femaleScn1a+/-animals in the F1 hybrid C57x129S6 background. We found increased mortality in femaleScn1a+/-regardless of age compared to their male counterparts (n = 120-125 mice/sex;p < 0.05). Interestingly, long-term video EEG recordings revealed the opposite for morbidity as seizure frequency and severity were escalated in adult maleScn1a+/-animals (n = 21-30 mice/sex;p < 0.05orp < 0.01). Adult femaleScn1a+/-mice, however, are more hyperactive (p < 0.05), which could be related to sleep impairment and contribute to the increased mortality despite decreased seizure morbidity. Overall, the phenotypic presentation ofScn1a+/-mice is sex-dependent and may have translational implications for therapeutic drug discovery and basic biology understanding in DS.