In a series of 24-hour ambulatory EEG recordings from 1,000 consecutive adult outpatients (44.5% with generalized and 55.5% with partial epilepsy, one recording per patient), the authors found only 46 (4.6%) activations of epileptiform discharges on awakening. All recordings came from patients with idiopathic generalized epilepsy, predominantly with juvenile myoclonic epilepsy and generalized tonic-clonic seizures on awakening. Multiple spike discharges that develop with an unusually delayed onset after arousal (more than 10 minutes) might help to discriminate juvenile myoclonic epilepsy.