IntroductionAppendicitis is a global disease affecting roughly 1 in every 12 people in the world, with the highest incidence between ages 10 and 19 years. To date, a wide variety of health outcomes have been reported in randomised controlled trials and meta-analyses evaluating treatments for appendicitis. This is especially the case in studies comparing non-operative treatment with operative treatment. A set of standard outcomes, to be reported in all future trials, is needed to allow for adequate comparison and interpretation of clinical trial results and to make data pooling possible. This protocol describes the development of such a global core outcome set (COS) to allow unified reporting of treatment interventions in children with acute uncomplicated appendicitis.Methods and analysisWe use current international standard methodology for the development and reporting of this COS. Its development consists of three phases: (1) an update of the most recent systematic review on outcomes reported in uncomplicated paediatric appendicitis research to identify additional outcomes, (2) a three-step global Delphi study to identify a set of core outcomes for which there is consensus between parents and (paediatric) surgeons and (3) an expert meeting to finalise the COS and its definitions. Children and young people will be involved through their parents during phase 2 and will be engaged directly using a customised face-to-face approach.Ethics and disseminationThe medical research ethics committee of the Academic Medical Center Amsterdam has approved the study. Each participating country/research group will ascertain ethics board approval. Electronic informed consent will be obtained from all participants. Results will be presented in peer-reviewed academic journals and at (international) conferences.Trial registration numberCOMET registration: 1119