This study aims at finding the relation between attention deficit hyperactivity disorder (ADHD) neuropsychological and neurophysiological tests. The study included 40 ADHD patients and 40 healthy control subjects. All patients and controls undergone clinical, electrophysiological assessment and neuropsychological assessment (patients only). Results revealed frequent electroencephalography (EEG) abnormalities, statistically significant difference in polysomnographic parameters and statistically significant difference concerning all event related potential (p300) test parameters in patients compared to control subjects. We concluded that ADHD is frequently associated with abnormal EEG changes, reduced amplitude and prolonged latency of p300 response, sleep disordered breathing and limb movement disorder.