Background: In clinical trials the selection of appropriate outcomes is crucial to the assessment of whether one intervention is better than another. Selection of inappropriate outcomes can seriously compromise the results of a trial. However, the process of selecting the most suitable outcomes to include can be complex. Objectives: To systematically review studies which address the process of selecting endpoints or outcome domains to measure in clinical trials in children. Methods: We searched relevant databases for studies involving the selection of outcomes for use in clinical trials in children. We also asked a group of experts in paediatric clinical research whether they knew of any other relevant studies. From these articles we extracted data regarding the clinical condition of interest, description of the method used to select outcomes, the people involved in the selection process, the outcomes selected, and limitations of the method as defined by the authors. Results: The literature search identified 8889 potentially relevant abstracts. Of these, 70 were retrieved, and 25 were included in the review. These studies described the work of 13 collaborations representing various paediatric specialties. Three groups utilised the Delphi technique and two the NGT to reach a consensus about which outcomes should be measured in clinical trials. Other groups used semi-structured discussion, and one group used a questionnaire-based survey. The collaborations involved clinical experts, research experts and industry representatives. Three groups involved parents of children affected by the particular condition. Conclusions: There are very few studies which address appropriate outcomes for clinical research with children and in most paediatric specialties, no research has been done. Among the studies which we did assess, very few involved parents or children in selecting which outcomes should be measured.