To clarify the effects of sleep on cortical irritability in benign adult familial myoclonus epilepsy (BAFME), we retrospectively compared epileptiform discharges of electroencephalographies (EEGs) between awake and sleep periods in 5 patients (mean age: 49.6 ± 20.3 years). We also analyzed polysomnography (PSG) of 1 patient. Epileptiform discharges were significantly more frequent during the awake period (1.3 ± 1.2/min) than those during light sleep stages (0.02 ± 0.04/min) (P < 0.05). Regarding PSG analysis, epileptiform discharges were also reduced during all sleep stages compared to those during awake periods. Our study suggests a relative reduction in cortical irritability during sleep in BAFME.