There have been major advances in the field of paediatric rheumatology over the last 15 years, which have included improvements in the classification of chronic arthritis, the most common chronic rheumatic disease in children and adolescents. A new classification was proposed by the International League of Associations for Rheumatology (ILAR) in 1995, which facilitated collaborative research and comparability of study results. According to the ILAR classification juvenile idiopathic arthritis (JIA) is a new term that encompasses the heterogeneous forms of arthritis of unknown cause, which begin before 16 years of age. The JIA classification identifies seven disease categories, which differ in their clinical presentation, outcome, and in some cases, genetic background, and which are characterized here on the basis of data from the national paediatric rheumatology database. Despite its usefulness for international research, the ILAR classification also has restrictions and further revision is therefore required. A special problem with a need for a solution is represented by the limited application in adult rheumatology.