We studied the long-term follow-up of patients with the diagnosis of "syncope of unknown origin," and their progression to epilepsy to gain a better understanding of the relationship between syncope and epilepsy, and to determine whether findings of the first syncopal attack have prognostic significance in relationship to the onset of epilepsy or not. Eighteen patients viith the diagnosis of syncope of unknown origin were evaluated for the possibility of becoming epileptic during a 4-year period, and four patients showed characteristic seizure disorder. There were no clinical or laboratory features that differentiated them from the nonepileptic group, except that they were all girls. The interval between the first syncopal attack and the typical epileptic seizure ranged between 7 and 19 months. Syncope of unknown origin could be the first sign of an epileptic disorder, especially in girls. Long-term follow-up extending up to 1 year is necessary to disclose the risk of becoming epileptic.