A total of 300 children aged five years and under, referred for routine EEG investigations, were included in this study. It was possible to obtain recordings during natural sleep in 250 of the 300 children, using stick-on electrodes. Of the 250 with natural-sleep recordings, 110 children had normal records both awake and asleep. In 73 cases the awake record was normal but the asleep record showed abnormalities, the most common being spike discharges (60 children). Of these 60 children, 52 had a history suggestive of epilepsy or of febrile convulsions. A further 27 children had recordings which were equally abnormal awake and asleep, and 37 showed abnormalities while awake but greater abnormalities while asleep. It is concluded that useful additional information can be obtained from the EEG if young children are encouraged to sleep naturally during the recording, and that this can be done without sedation, even in a busy, routine EEG department.