This document has been developed by the ad hoc group for the development of implementing guidelines for Directive 2001/20/EC relating to good clinical practice in the conduct of clinical trials on medicinal products for human use, chaired by the European Commission. The document provides recommendations on various ethical aspects of clinical trials performed in children from birth up to the legal age of adulthood. This will contribute to the protection of all children who are the subject of clinical trials. As the approval of clinical trials, including ethical approval, is performed by the Member States, any recommendations on ethical aspects of clinical trials in children will also facilitate a harmonised approach to the application of the clinical trials directive across the EU, thereby facilitating the conduct of clinical trials in the EU and in whichever country the paediatric trial occurs. The protection against the risks of research in such a vulnerable population is paramount whilst this should not lead to denying them the benefits of research. Children are not small adults and there is a need to carry out specific trials that cannot be performed in adults. In general, children (minors) are unable to consent (in the legal sense) but their assent should be sought using age appropriate information. Ethics Committees need paediatric expertise to balance the benefits and risks of research in children. The lack of legal ability to consent has implications on the design, analysis and the choice of comparators used in trials, which should only be performed by trained investigators with paediatric experience. Pain, fear, distress and parental separation should be prevented and minimised when unavoidable. The neonate represents the most vulnerable of all paediatric age groups and requires even more careful review. Finally, various other aspects relating to the performance of trials in children are discussed.