Despite the introduction of better-structured programmes for paediatric anaesthesia training and the development of some recommendations for paediatric anaesthesia services, the incidence of severe critical events in children is still unknown in Europe. Considering that the major life-threatening complications following general or regional anaesthesia are uncommon, it is therefore crucial to consider a large multinational, multicentre trial in order to establish a realistic statistical estimation and identify the risk factors for severe critical events. Thus, this prospective observational multicentre cohort study is designed to identify the incidence and potential risk factors of severe critical events in children undergoing anaesthesia in Europe.