Melatonin is a hormone secreted from the pineal gland. The circadian rhythm of melatonin changes according to age and it's production decreases with older ages. Melatonin is an antioxidant, antinociceptive, hypnotic, anticonvulsant, neuroprotective, anxiolytic, sedative, analgesic and has a preventive effect of delirium in intensive care. Irregularity of melatonin secretion causes a sleep irregularities, psychosis in intensive care unit and some behavioral disorder. It has been demonstrated that oral exogen administration of melatonin was effective on preoperative anxiety.