Following our original description of generalized epilepsy with febrile seizures plus (GEFS+) in 1997, we analyze the phenotypic spectrum in 409 affected individuals in 60 families (31 new families) and expand the GEFS+ spectrum. We performed detailed electroclinical phenotyping on all available affected family members. Genetic analysis of known GEFS+ genes was carried out where possible. We compared our phenotypic and genetic data to those published in the literature over the last 19 years. We identified new phenotypes within the GEFS+ spectrum: focal seizures without preceding febrile seizures (16/409 4%), classic genetic generalized epilepsies (22/409 5%), and afebrile generalized tonic-clonic seizures (9/409 2%). Febrile seizures remains the most frequent phenotype in GEFS+ (178/409 44%), followed by febrile seizures plus (111/409 27%). One third (50/163 31%) of GEFS+ families tested have a pathogenic variant in a known GEFS+ gene. As 37/409 (9%) affected individuals have focal epilepsies, we suggest that GEFS+ be renamed genetic epilepsy with febrile seizures plus rather than generalized epilepsy with febrile seizures plus. The phenotypic overlap between GEFS+ and the classic generalized epilepsies is considerably greater than first thought. The clinical and molecular data suggest that the 2 major groups of generalized epilepsies share genetic determinants.