This paper provides a short overview of the Danish health care system and the organization of care for type 2 diabetes patients in Denmark. It also describes the supplementary data sources that are used for collection of baseline data in the nationwide Danish Centre for Strategic Research in Type 2 Diabetes (DD2) Project. The Danish National Health Service provides tax-funded medical care for all 5.6 million Danish residents. The health care system is characterized by extensive individual-level registration of data used for planning, administration, quality improvement, and research. It is estimated that there are currently at least 250,000 individuals with known diabetes in Denmark (approximately 4.5% of the Danish population), of which an estimated 80% are followed and treated by their general practitioners and approximately 20% are followed at hospital specialist outpatient clinics. These health care providers form the basis for recruiting diabetes patients in the DD2 project, and the data sources that these providers use in clinical practice give access to important supplementary patient data. The DD2's patient-enrollment system is designed to be fast and simple, and thus only collects primary interview data that cannot be extracted from already existing data sources. Thus, in addition to an online DD2 questionnaire filled out by general practitioners and hospital physicians at the time of patient enrollment, supplementary data are obtained from the Danish Diabetes Database for Adults, a nationwide clinical quality improvement registry. Both hospital physicians and a growing number of general practitioners routinely report data to this database. For general practitioners, the Danish General Practice Database acts as an important feeder database for the Danish Diabetes Database for Adults and thereby also for the DD2 project.