This chapter describes the differential diagnosis, treatment, and outcome for severe myoclonic epilepsy of infancy (SMEI) or Dravet syndrome (DS). The frequency of convulsive seizures seems to correlate with the severity of developmental delay, suggesting that DS might be considered as a true epileptic encephalopathy. The frequency of detectable mutations in DS is around 70-80%; truncating mutations account for nearly 50% of the abnormalities with the remaining comprising splice-site and missense mutations. The repetition of febrile seizures and/or the prolonged convulsions with unilateral clinical features are clues orienting towards a diagnosis of DS. Children may manifest myoclonic seizures at onset and be misdiagnosed as having benign myoclonic epilepsy of infancy. Valproic acid, benzodiazepines, and topiramate have been proven to have some efficacy. Mortality rates are at around 16%, mainly as a result of sudden death or seizure-related accidents.