This thesis provided the first results of the Dutch Pediatric and Adult Registry of Diabetes (DPARD), a nationwide registry including children and adults treated for diabetes mellitus in outpatient clinics across the Netherlands. Diabetes mellitus requires high-quality diabetes care due to its complex and chronic nature as well as its complicated disease course. Diabetes registries may serve by measuring and comparing clinical outcomes and highlighting variations in care where gaps in delivered care are present, and quality improvement is needed. Quality of care can be assessed using quality indicators, defined as standardized, evidence-based healthcare quality measures. Quality indicators comprise structure, process, and outcome indicators. Structure indicators give information about preconditions of high-quality care, process indicators gain insight into healthcare processes, and outcome indicators describe outcomes of delivered care. In DPARD, structure, process and outcome indicators have been recorded since 2020. Indicator results from hospitals are provided to healthcare providers using online dashboards, benchmarking outcomes against the national average. This thesis consists of three parts focusing on the value of diabetes registries worldwide, including DPARD as well as the implementation of DPARD (Part I), the current status of Dutch outpatient diabetes care assessed by use of DPARD (Part II), and healthcare utilization in Dutch outpatient diabetes care (Part III). Combined, this thesis provides a clear and detailed view of the added value of systematically recording daily diabetes care.