Sleep deprivation (SD) is a known activator of epileptiform EEG activity in patients with epilepsy. In the workup of these patients, EEG recordings are performed following SD both in the awake state and during sleep. The latter significantly increases the duration and the cost of the examination; the specific yield of sleep tracing in single-session wake-sleep record after SD has not been evaluated in adult patients. Our study tried to answer this question, analyzing consecutive recordings of 76 adult patients who had an epileptiform abnormality in the SD record. Thirty-five of the patients were treated with antiepileptic drugs at the time of the study. After SD of 24-26 h, 1000-1500 mg of chloral hydrate were administered; an 18-channel standard awake EEG was performed, followed by 30 min sleep recording. Epileptiform activity was recorded in the wake part only in 7 (9%, 3 focal, 4 generalized); in 39 (51%) the activity was seen in both awake and sleep parts (21 focal, 5 focal with secondary generalization and 13 generalized); and in 30 (40%) it was found in the sleep part only (23 focal, 1 focal with secondary generalization and 6 generalized). Whenever epileptiform activity was apparent in both parts of the recording, its configuration and localization were identical in the sleep and the wake EEGs. This phenomenon was observed in both treated and untreated patients. In combined wake-sleep recording following SD in adults, sleep tracing may reveal epileptiform activity not demonstrated during the preceding wake EEG. However, if epileptiform activity appears already in the wake recording, subsequent sleep tracing may be redundant.