Background: Since sleep may affect information processing and therefore event related potentials (ERPs) an increased P300 latency and reduced amplitude are expected to be present when sleep is disrupted and shortened. Objective: This study aims at 1) Comparing evening to morning ERPs in controls, insomnia and sleep related breathing disorders (SRBDs) to explore the impact of good or bad sleep on ERPs. 2) Shedding the light on ERPs affection in patients with SRBDs and insomnia. 3) Assessing the association between the severity of subjective and objective sleep alterations and the changes in amplitude and latency of ERPs.Methods: 30 patients suffering from SRBDs and insomnia were subjected to polysomnography, as well as visual and auditory ERPs administered twice, pre-sleep and post-sleep. 15 age and sex matched healthy subjects were considered control group.Results: We found significant decrease in ERPs latencies, and increase in their amplitudes in the morning in control group, but neither decrease in morning ERPs latencies nor increase in their amplitudes were observed in patients. Evening ERPs were not significantly different among the three groups. Morning ERPs in SRBDs had longer latencies and smaller amplitudes with respect to controls. Evening to morning difference comparison revealed the subtle ERPs abnormalities in insomnia.No significant correlation was found between the changes of ERPs in patients and their Epworth sleepiness scales scores and polysomnographic data.Conclusion: Normal uninterrupted sleep greatly enhances ERPs. Multiple P300 measurements especially in the morning provide more sensitive marker for assessment of sleep effects on attention processes. The difference between evening and morning ERPs is very sensitive parameter and can detect subtle abnormalities especially in insomnia patients. Neither subjective nor objective estimates of sleep continuity can strongly explain the changes in the magnitude of ERPs.