The circadian and ultradian sleep and sleep-wake cycle significantly influences the expression of ictal and/or inter-ictal electroencephalographic and clinical manifestations in epileptic patients. Epileptiform discharges are tended to propagate during NREM sleep, contrastly, REM sleep is resistant to propagation of EEG discharges. This article is focused on clinical practical importance of the relationship between sleep and epilepsy. Interictal and ictal EEG discharges and sleep-wake cycle, sleep abnormalities in epileptics, clinical usage of sleep or sleep deprivation EEGs, effects of anti-epileptic drugs on sleep were discussed briefly.