Postoperative agitation and emergence delirium describe a spectrum of symptoms of early postoperative negative behavior, in which the child experiences a variety of behavioral disturbances including crying, thrashing, and disorientation during early awakening from anaesthesia. The symptoms are common with a reported incidence of approximately 25%. Some clinical trials have studied the effect of prophylactic oral melatonin for reducing the risk of emergence agitation in children, some finding a considerable dose-response effect. Melatonin has a low bio-availability of approximately 15 %. The safety of exogenous melatonin for pediatric patients has been studied with no apparent serious adverse effects, even at repeated short-term use of high doses of intravenous melatonin. The aim of this clinical trial is to investigate the prophylactic effects and safety of intravenous melatonin administered intraoperatively for prevention of postopreative agitation and emergence delirium in children after an elective surgical procedure. The study is designed as a randomised, double-blind, placebo-controlled clinical trial.