INTRODUCTION. Reporting of outcomes in groin hernia trials is inconsistent and poorly defined thereby limiting the production of high-quality meta-analyses. Outcome reporting can be standardised and improved through consensus-based development of a core outcome set, which is a minimum set of outcomes recommended to be reported in all effectiveness trials within a specific field of research. We aim to develop a core outcome set for effectiveness trials within clinical groin hernia research. METHODS. The study is divided into three phases. Phase 1 is an update of a systematic review on outcome reporting in groin hernia trials, which will identify relevant outcomes of groin hernia repair. In Phase 2, we will conduct multiple Delphi rounds to achieve consensus on which of the identified outcomes are most important. These Delphi rounds will involve important stakeholders in the field, i.e. patients, surgeons and researchers. In Phase 3, we will organise a consensus meeting to determine the final contents of the core outcome set. The meeting will involve the expert members of the study Steering Committee and invited key stakeholders. Data collection permissions and ethical approvals will be sought from the appropriate national and local authorities. CONCLUSION. Development of a core outcome set for groin hernia trials is necessary and feasible.