Objective The poor sleep quality of epileptic patients may be partly due to the occurrence epileptiform discharges (EDs).We observed the number of interictal discharges in each sleep stage and explored the associations between EDs and sleep phases in epilepsy patients.Methods Two hundred and forty epileptic patients and 213 healthy volunteers were enrolled in the current study.For all subjects,video-electroencephalogram monitoring and 24 h-night polysomnography were conducted to detect EDs and analyze the sleep structures.Results EDs were detected in 88.7％ (213/240) of epilepsy patients with the most frequent cases from the temporal lobe.The EDs detected during waking,sleeping,or both waking and non-rapid eye movement (NREM) sleep stage accounted for 20.6％ (44/213),40.4％ (86/213),and 38.9％ (83/213) of the total patients,respectively.The total sleep time and time spent in REM were similar between the epileptic patients and healthy volunteers.However,epileptic patients spent a significantly longer mean sleep time in NREM Ⅰ-Ⅱ ((304 ±39) min versus (225 ±29) min,t =3.51,P =0.000) and less in NREM Ⅲ-Ⅳ ((49 ± 7) min versus (133 ± 17) min,t =2.30,P =0.000) than healthy volunteers.Furthermore,asymmetric sleep spindles and fragmentary sleep structure as well as high inversion frequency were found in epilepsy patients,respectively.Conclusion Combination of long-term video electroencephalogram with polysomnography is a useful method to analyze associations between EDs and the sleep-wake cycle.This strategy can also help identify the nature of sleep disorders in epileptic patients,which may improve the treatment efficacy.