Severe myoclonic epilepsy of infancy (SMEI) is a newly recognized epileptic syndrome. It is characterized by multiple febrile seizures, often prolonged, subsequent development of uncontrollable mixed-myoclonic seizures, and, eventually, psychomotor retardation. Drugs for myoclonic epilepsy--valproate (VPA), the suximides, and the benzodiazepines--have been shown to be useful in SMEI. Among children with seizures in the National Institute of Neurological and Communicative Disorders and Stroke Collaborative Perinatal Project (NCPP), one individual with SMEI was identified. This finding from the NCPP suggests that the incidence of SMEI is approximately 1 in 40,000 children. Such an incidence is supported by observations at the Texas Tech University Health Sciences Center.