We report eight sporadic cases of typical Angelman syndrome (AS) associated with chromosome 15q12 deletion. Age at first visit was 3-35 months (average 18 months), and follow-up period was 4-20 years (average 14.1 years). The characteristic features of epilepsy in AS are (a) seizure onset in early childhood (8 of 8); (b) evolution of seizure type with age (8 of 8); (c) EEG abnormality changes from high-voltage slow bursts (HVS) in infancy to diffuse spike and waves in middle childhood (4 of 5); (d) atypical absence seizures (8 of 8), often occurring as atypical absence status (4 of 8); and (e) diminution of seizure discharges and clinical seizures after puberty (7 of 7). We believe that AS may frequently exist in the intractable epilepsies of childhood with severe mental retardation. We stress the importance of AS as one of the main etiologic background diseases of the intractable epilepsies with infantile onset such as West syndrome, Lennox-Gastaut syndrome, and others.