Background: Type 2 diabetes is characterised by abnormal glucose metabolism, and treatment is aimed at normalising glycaemia. Outcomes measured in clinical trials should be meaningful to patients, health care professionals and researchers, yet there is heterogeneity in the outcomes used across trials of glucose-lowering interventions. This inconsistency affects the ability to compare findings and may mean that the results have little importance to health care professionals and the patients for whom they care. The SCORE-IT study aims to develop a core outcome set (COS) for use in all trials of glucose-lowering interventions for people with type 2 diabetes. Methods/design: This study will involve three key stages in the development of a COS: (1) A list of outcomes will be identified from multiple sources, specifically registered clinical trials, online patient resources, the qualitative literature and landmark studies identified by a Study Steering Committee. (2) The list of outcomes will be scored by multiple stakeholder groups in a two-round online international Delphi survey. (3) The results of the online Delphi will be summarised and discussed at a face-to-face consensus meeting with representation from all stakeholder groups. Discussion: The SCORE-IT study aims to develop an internationally relevant set of core outcomes for use in future trials of glucose-lowering interventions for type 2 diabetes. The use of a COS will improve the consistency of outcomes, allowing results of studies to be compared and combined and for new effective treatments to made available more quickly. Trial registration: The COS study, of which this is a part, is registered in the Core Outcome Measures in Effectiveness Trials (COMET) database, http://www.comet-initiative.org/studies/details/956. Registered January 2017.