This is a pre-print of our Delphi study to develop a person-centered outcome set for routine diabetes care in Europe: Standardized collection of patient-reported outcomes (PROs) integrated with clinical data can empower patients and enhance diabetes care. We sought to develop a person-centered outcome set for type 1 and type 2 diabetes containing patient-relevant and clinically meaningful outcomes that is feasible and sustainable in international healthcare settings, and will be implemented and tested in Europe as part of the H2O project. A questionnaire-based three-round Delphi exercise based on previously identified outcomes was undertaken to reach consensus on the outcome set. The here developed person-centered outcome set for diabetes was agreed by four international key stakeholder groups and allows for collecting standardized patient-relevant diabetes outcomes at scale to inform individual and population level healthcare decision-making.