The nation-wide Danish Registry of Childhood Diabetes and associated biological bank were established in 1996. All children diagnosed with insulin-dependent diabetes mellitus (IDDM) under the age of 15 years are included. In the period 1996-2004 the incidence of IDDM in childhood and adolescence (0-15 years) has increased by 3.5% per year and was 25.7/100.000 in 2004. The average measured glycosylated haemoglobin (HbA1c) value has decreased over the period and was 8.4% in 2005. A registry of type 1 diabetes with a high degree of completeness is feasible, provides useful information about the quality of patient care and is a valuable resource for research.