Genetic (generalized) epilepsy with febrile seizures plus is a familial epilepsy syndrome with marked phenotypic heterogeneity ranging from simple febrile seizure to severe phenotypes. Here we report on a large Israeli family with genetic (generalized) epilepsy with febrile seizures plus and 14 affected individuals. A novel SCN1A missense mutation in exon 21 (p.K1372E) was identified in all affected individuals and 3 unaffected carriers. The proband had Dravet syndrome, whereas febrile seizure plus phenotypes were present in all other affected family members. Simple febrile seizures were not observed. Phenotypes were found at both extremes of the genetic (generalized) epilepsy with febrile seizures plus spectrum and distribution of phenotypes suggested modifying familial, possibly genetic factors. We suggest that families with extreme phenotype distributions can represent prime candidates for the identification of genetic or environmental modifiers.