A retrospective method was used to estimate the incidence of recurring motion-sickness, cyclic vomiting and abdominal pain considered as different manifestations of a so-called periodic syndrome in 100 migraine sufferers, 100 epileptics and 100 control subjects in the pediatric age group. Such recurrent symptoms are significantly more frequent in those suffering from migraine than in the other two groups. Examination of subgroups of patients affected by particular forms of migraine (classical and common) and of epilepsy (generalized seizures, simple partial seizures, complex partial seizures) contributed little new to our understanding of the nature of periodic syndrome. It is concluded that the above symptoms of periodic syndrome should generally be considered as manifestations of a migrainous rather than of an epileptic disorder.